Red Alliance is an indie shooter that reminds one mostly of Half-Life with slight nods to F.E.A.R. and S.T.A.L.K.E.R. series and plays just about any arcade shooter from 2000's. It boasts a pretty linear campaign with an adventureous feel to it, clocking around three hours at most.
This guide's primary aim is to point out the collectibles and secrets, of which there are many to find or discover along the way. Apart from 'Tough Guy' (which requires a second run), all of the achivements can be earned in a single playthrough, with the help of a bit of saving and loading. As long as you do not uninstall it, the game tracks your collectible progress in a profile file so it is possible to catch them later (by way of giving the campaign another go, replaying a specific chapter or loading a level directly) if you happen to miss any of them the first time around.
All of the screenshots provided in the guide were taken with 'Player Graph' option on, so that a player (also with his 'Graph' turned on) referring to them may compare his coordinates in any given map to the coordinates shown in any given shot. Note that with the update in August 2019, the chapter Urban Hazard was given a new look - instead of day time, it now takes place in the evening. Thus the screenshots may differ from what you see in game, but the coordinates are more or less the same, since there aren't any changes to the item placement. Alongside the chapter names, map names are also provided on a basis of necessity in achievement pointers so that players may use the information to directly jump to specific point in the game.
For reference, here is a breakdown of all the chapters and maps in game proper:
You can load a map directly by using the 'map' command in the console. As in, 'map horror_office', without the quotes. Apart from the 'map' command, there are a bunch of others that may prove helpful for tracking and referral purposes:

• achievements_print: Prints a list of all the achievements in the game and and shows your progress towards them with counters for collectibles.
  
• stats_print_all: Prints a list of global gameplay stats with specific detailment on weapons usage. Useful for checking up what you have got a hold of.
  
• maps: Prints a list of all the maps in the game, in gameplay order.
  
• weapons: Prints a list of all the weapons in the game.
  
• status: Shows the name of the map you are in as well as your coordinates.

You can also cheat your way through the game by using the console. However, enabling cheats locks you out of gaining achievements so they are left out of this guide.
The achivements are grouped as 'Story Related' (which are unmissable), 'Optional / Collectibles / Secrets' (which require more effort and are missable), 'Weapons' (which is about completing your weapon collection) and 'Kills' (which is about, well, shooting stuff) in the guide. Achievements under each group are ordered by your first chance to get them (or your first step towards them, in case of a collectible one).

You get this achievement when you finish the 'Prologue' chapter.
This one is granted when you get to the end of the chapter 'The Great Escape'.
Finishing the chapter 'Urban Hazard' grants you this one.
Midway through the chapter 'Ad Stygem', just before you enter a ventilation duct to progress you pick up another flashlight from the ground, this one pops up then.
Near the end of the chapter 'Reminiscence' you need to save Stanko, Paul and other captives of Dr. Grey from a gas attack. Doing so grants you this achievement.
It unlocks when you reach the credits screen, regardless of the difficulty level.
Vortex Run is an alternate take on the campaign that is unlocked after finishing a standard run once. You start Vortex Run with a baton and unlimited Vortex X at hand, of which the second still requires a reload every six shots. You cannot pick up or use any other weapon apart from these two, although you can still utilize the health kits found throughout the game. This mode is only playable in a fixed 'Hard' difficulty. There are no checkpoints, saving is not allowed and you only have one chance to get through the whole of it. As a side note, you are also free to kill any NPCs that you come across: it does not impede your progress in any way. Still, Stanko may be needed for the final area (as he is tied to a script), so it is best to spare and protect him.
Although it may not sound so, the run is not that difficult as long as you react quick enough and have a steady aim. Guards and zombies disintegrate with a single shot, while heavies take two shots (one, if you go for the head). Do not rush it, do not take risks; take it slow and methodic, use cover and get those 'special' health kits along the way. Be extra careful through the Outpost, the storage area and the final showdown. It takes around an hour to complete the game in this mode, assuming you know your way around.
For the final showdown, taking cover by the metal crates next to the locked door and utilizing the two barrels next to them (as shown below) may be a good strategem. Disintegrating the metallic panels covering the railings of the ladders before going down the area also helps, as the spawning guards tend to take cover beyond them. For the two zombie waves, you can hop on the metallic crates next to you and easily pick them off from there, without risking your health.
You get this achievement when you finish the Vortex Run.

The drink dispensers found throughout the game are actually interactable. Of the available selection, one of the buttons serves you a 'Dank Magic', unlocking this achievement in the process. As shown below, one can be found as early as the chapter 'Prologue' (prologue_1).
To unlock this one, you need to trigger dialogues or monologues that takes place behind closed doors. Five of them can be found throughout the chapter 'Prologue', their door numbers being 131, 135, 160, 166 and 178. When you reach the chapter 'Red Alliance', be sure to check on the unmarked wooden doors throughout the rebel base, as the other eight are behind those.
You need to pick up and drop ten intact bottles to a trash bin. Best to be done early. As shown below, there is a bin in the second area of the chapter 'The Great Escape' (prison_2) with ten bottles in the same room.
Additional info: A definite nod to Half-Life², i.e. the scene in which a civil protection officer orders the player to pick up a soda can from ground and put it in the trash bin.
Throughout the game you come across orange coloured, 'special' health packs that restore 40 hitpoints and that can also take you above 100%. Although a few of them are out in the open, most are pretty well hidden. Refer to the pointers and shots below to locate them.
SHP #1 - The Great Escape (prison_3)
In a breakable vent to the your left, right above a bookcase.
SHP #2 - Urban Hazard (city_2)
On your way to the train station, behind a bank to your right.
SHP #3 - Red Alliance (mountains_2)
In the bathroom of the rightmost apartment on the first floor of the three-storied building at the outpost.
SHP #4 - Red Alliance (mountains_3)
Next to a flaming barrel to the left, in the square where you encounter a rather large group of guards.
SHP #5 - Ad Stygem (horror_sewer)
Hidden behind a barrel just before leaving the sewer system behind.
SHP #6 - Descent (horror_construction)
Right in front of you as you make your way on the planks. Take note that the plank on which the kit resides breaks when you step on it, leaving you at the mercy of the zombies lying in wait; so it is wiser to get the kit beforehand by shooting it from below.
SHP #7 - Descent (horror_construction)
In the control room you can reach by moving up the ladder at the storage area. This one may be harder to get if you opt for a stealthy approach in this section.
SHP #8 - Reminiscence (horror_labs)
In a secret room behind a force field, after rescuing Stanko and Paul.
SHP #9 - A Means to an End (boss_battle_1)
Hidden from sight on a water pipe, just after you split up with Stanko.
SHP #10 - A Means to an End (boss_battle_1)
In the storage room reachable through an office, right where you find the scientists.
SHP #11 - A Means to an End (boss_battle_2)
In the final area where you make a stand, behind some metallic crates to the left.

This one requires you to kill all the citizens you come across (that can be hurt) throughout the game. You encounter eleven of them through the chapter 'Urban Hazard' (city_1/2) while the rest of them are to be located in the next one, 'Red Alliance' (mountains_2/3). Apart from the mentioned seventeen, you can also kill Nikolai (and get his Firefly) as well as a sleeping civilian (in one of the containers in the garage) that you encounter in the first map of the chapter 'Red Alliance' (mountains_1), but they are not counted towards the achievement.
They are listed and shotted below in the order you encounter them.
As shown in the eighth shot of the section above, you encounter a civilian running from two guards while exploring the apartments in the chapter 'Urban Hazard' (city_2). Kill the two guards before they finish off the said civilian and proceed to talk with him to get the achievement. Be sure to pick up the key on offer for the next achievement and kill the guy after that for your progress in the previous one.
After taking the key offered by the civilian you saved from the oppressors, head for apartment 61 at the end of the hall. Unlock the door to get the achievement, listen to radio messages and don't forget to try out the Makarov tucked under the bed.
Additional info: Apartment 61 is a replica of the starting room of the first playable version of Red Alliance, offered to the public as a demo back in 2013. The radio messages and the Makarov pistol to be found within also originates from the said build.
Continuing down the same apartment hallway from the previous achievement, you come across apartment 68. Ring the bell to get an angry reply from the resident. Ring it four times more to get the achievement. Note that doing so changes your prisoner outfit to an Adidas zip jacket and spawns three thugs in the hallway for you to deal with.
Additional info: A reference to a Russian subculture. Search 'gopnik', if you are interested.
Halfway through the rebel base in the the chapter 'Red Alliance' (mountains_1), you are offered two outfits that you can change into. If you don one, you get this.
In the chapter 'Red Alliance' (mountains_1), Ratko wants you to follow him downstairs after briefly discussing the rebels' next move with Yan. Do so, but be sure to also check the lowest level before passing through a storeroom with him. There you find another rebel named Nikolai. Catch up with Ratko in the garage, in which there is a blue colored container to the left. Find your way into it, grab one of the bowling balls contained within and return to Nikolai with that in hand to unlock this achievement.
Additional info: A definite nod to Grand Theft Auto IV. The character Nikolai is modelled after Niko Bellic, the protagonist of GTA IV. His cousin Roman repeatedly invites Niko for a game of bowling during the phone conversations between the two over the course of the game.
Midway through the chapter 'Red Alliance' (mountains_2), you come across the Oppressive Unit's outpost which consists of a three-storied building to your left and a single-storied depot to your right. The objective here is to disable four wall panels scattered across these buildings to open the electronically-locked gate which blocks your way. Opting for a stealthy approach grants you this achievement (when you find yourself at the other side of the locked gate). However, the next two achievements are also tied to this section of the game and one of them is not possible to get while you are undercover. So save beforehand, go for stealth first; reload and go in guns blazing next (or vice-versa) to unlock all three in a single run.

From the front door of three-storied building in the Oppressor's outpost, take the right hallway to find a radio on a crate in front of a window. Interact with the radio to get the achievement. May be harder to do coupled with a stealthy approach in the said section, but if you manage to do so, there is a little surprise for you.
Additional info: A definite nod to S.T.A.L.K.E.R. series of games. The track on offer is 'Bandit Theme' from the said series. Check the unofficial wiki[stalker.fandom.com] for details.
Taking your time in the Oppressor's outpost, look for a key located on a table in the midst of the third floor of the three-storied building. After taking the key, make your way to the basement level and unlock the only door to be found there to get the achievement. Be sure to try out Valik stored in an open locker to your right (for your weapon collection progress). Here is also a locked door with an electronic keypad next to it, beyond which you can listen to another radio message. If you can't figure it out from the given hints, the code is: 102400.
Additional info: The two vehicles to be found behind the electronically-locked door are earlier variants of the drivable buggy in the final version of the game, one dates back to 2016 while the other goes as back as 2014. The radio message also originates from a 2014 build.
Right in the beginning of the chapter 'Ad Stygem' (horror_sewer) you find yourself in a sewer system. Look to your left for a barricaded door hidden behind three crates. Break them all to find another electronically-locked door tied to a keypad. Figure out the code to the door (it is 834928, if you can't) and listen to the radio message found in the room behind it to get the achievement. Check out Firefly located right next to the radio, which is a shotgun that fires incendiary shells, for your weapon collection.
Additional info: The room behind the electronically-locked door is a replica of the map that is used as the menu background in the 2013 build. The radio message within is also another one from that version.
Midway through the chapter 'Deleterious Entity' (horror_office), you find yourself disturbed by unnatural phenomena, apparently caused by a ghastly zombie lurking in the area. Kill him, and the achievement is yours.
In the chapter 'Descent' (horror_construction) you have to make your way through a crate-filled maze with zombies in wait at every turn. A half-open door to your left can be seen behind a fence as you find yourself in this section. Reaching the door requires smashing two breakable crates which can be found near the end of the maze stashed on top of the unbreakable ones. Listen to the radio message found within to get the achievement. While you are in there, look for a Mini Uzi on top of a crate for your weapon collection.
Additional info: This room is a replica from the 2013 build. The radio message and the unique Mini Uzi also date back to the same build.
Midway in the chapter 'Descent' (horror_construction) you have a chance to catch a guard unaware, as shown in the first shot below. You have to stealth-kill him and opt for the ladder shown in the second shot without alerting anyone to your presence. Following this upper path through the storage area to its end grants you the achievement. Take note that choosing the stealthy approach locks you out of getting the next achievement, so save and load as needed.
As you enter the above mentioned storage area, you come across two guards in small talk, unaware of your presence if you manage to stealth-kill the guard you encounter right before them. Just interact with the console to your right which can be seen in the shot below to drop the container hanging above on top of them and get the achievement. Mind that doing so blows your cover.
You come across Vortex X midway through the chapter 'Reminiscence' (horror_labs), on top of a table in the same room where you contact the rebel base over the radio. Pick it up.
Midway through the chapter 'A Means to an End' (boss_battle_1), you make your way through a hallway with zombies behind bars on both sides. While you are busy fighting the guards in the next room, Dr. Grey unlocks the said cells and zombies join in the fray. Make haste, pick up the keycard from the control room to your left and unlock the next gate with it, ignoring the zombies in the process. You come across a scientist begging for his life right after passing through the gate. Let the zombies tear him up to get the achievement.
After dealing with the above-mentioned zombies, look for a computer in the office on the right with this minigame running on it. The object of the game is to reach the top of the tower. If you manage to do so, you get both the achievement and the Luger pistol, which is needed for a complete weapon collection.

The game's arsenal consists of twenty-five weapons, of which some of are also used by the Oppressors and thus can be found all-around, and others are rare, which are harder to come by, or unique, which are one-of-a-kind and well-hidden. You need to get a hold of every one of them at least once to get these two achievements.
For reference, here is a breakdown of all the weapons to be found:
They are listed and shotted below in order of (first) appearance.
A few things to keep in mind about the weapons:

• Picking up the unique Pokoinik also counts for MP-433, but not vice-versa.
  
• Picking up an M4A1 or M4A1-K counts for both.
  
• Picking up a scoped or non-scoped SV 98 counts for both.
  
• Picking up a rare Valik also counts for AS 'Val', but not vice-versa.
  
• Picking up a rare Firefly also counts for Shorty 12G, but not vice-versa.
  
• If you miss any weapon and want to save yourself from the hassle, you can load up test_level_5, which houses all the weapons in the game for testing purposes.

Looking for Guardian (prison_4):
Searching for Pokoinik [the first] (prison_3):
(Note that there was a special health pack here before the August 2019 update, hence the shot.)
Searching for Pokoinik (the second) (mountains_2):
Stopping by Povstanec (mountains_2):
Uncovering the crowbar (horror_office):
Reaching for Vortex X (horror_labs):

Self-explanatory and pretty easy to get. Use a rocket in the building where you find the final three civilians needed for the Oppressive Regime achievement interrogated by two guards in the third part of the chapter 'Red Alliance' (mountains_3). Alternatively, use a grenade on the zombie crowd that spawns below you as you are making your way on the planks in the chapter 'Descent' (horror_construction).
You drive a buggy throughout the second part of the chapter Red Alliance (mountains_2/3). That is your only chance to drive over a total of twenty Oppressors to get this achievement. Saving and loading may be needed.
Heavies are the tougher Oppressors that are equipped with SCAR-L's. This achievement comes naturally as you encounter more than ten of them over the course of a single run through the game.
Another self-explanatory one. You may go for the first one you encounter that patrols the road between the two buildings that forms the Oppressors' outpost you come across in the chapter 'Red Alliance' (mountains_2), after taking care of the other guards around for an easier brawl on your end. It is also possible to weaken a Heavy with other weapons first - just be sure to deliver the final blow with the baton. - Hats off to Muckelchen for the tip.
You get your first chance to grab a Desert Eagle in the chapter 'Deleterious Entity' (horror_office). Blow off heads with it until the achievement pops up.

Unlike many indie shooters, Red Alliance comes equipped with a fully-featured console. As per default, the console can be accessed by using the " (tilde) key, as long as it is enabled in the game options. The full list of the available commands can be found in the text file 'consoleCommands' which is in turn located in the folder Red Alliance\Assets\Resources.
As mentioned in the 'Foreword' section, cheats are left out of this guide (as enabling them disables achievements) and are not to be revealed in this section (apart from a specific one). Alongside the cheats and developer helpers, variables related to game options which can also be customized from the menu or the ones that change the intended look and feel of the game are not covered by this guide.
The variables and commands below can be used to tweak the game further. Note that every variable's default value can be seen in the console while typing it.
Resetting the gameplay stats

• stats_reset_all
  
• stats_reset_current
  
• stats_reset_global
  
• stats_reset_weapon

Customizing the position / angle of the weapon model

• viewmodel_offset
  
• viewmodel_offset_x
  
• viewmodel_offset_y
  
• viewmodel_offset_z
  
• viewmodel_reset

Customizing the crosshair

• crosshair_color
  
• crosshair_dynamic
  
• crosshair_gap
  
• crosshair_height
  
• crosshair_outline
  
• crosshair_outline_color
  
• crosshair_style (0/1/2)
  
• crosshair_width
  
• crosshair_reset

Customizing the skin for the hands

• player_skin (between 1 and 8)

Cinematic Mode
An interesting mode that can be toggled on and off through the console is the cinematic mode. It is akin to the photo mode which can be found in most of the AAA shooters, wherein you can customize the first-person view to your liking which can be used to set up a scene for your screenshots. To use the cinematic mode, the cheats must be enabled first (desu 1).
Typing in the command cinematic_mode 1 enables 'noclip' and 'notarget' at the same time, meaning that you can fly / move through the boundaries of the environment and the enemies do not attack you unless provoked. As seen in the shot above, further options are also available through a secondary panel, which can be turned on by typing cinematic_tab 1 in the console.

Kudos to the developer Roman Agapov for the enjoyable experience and his helping out with the guide (which wouldn't be complete if not for his feedback).
The 2013 build of Red Alliance referred throughout the guide, which is more-or-less a very early alpha, as well as another demo from 2015 which includes the earlier versions of the chapters 'The Great Escape' and 'Urban Hazard' from the game, are available as free downloads on its IndieDB page. Check them out here.
Feel free to contribute or ask away through the comments section.