You can Download and Activate this mod from inside Quake 1 on Steam. Yes, I know, it's amazing!
The parameter you need is:

Single player is easy, once you got the mod, just using Menu or console:

It is possible, with a pair of hacks, to create Modded lobby from inside Quake, and invite Steam friends directly.
After opening Multiplayer menu you have to switch to mod by typing in console:
Then close console and continue using GUI as before.

Game is basically horde-surviving hero tower-defense mod for Quake.

You can die as much as you want, but if the Heart is destroyed - it is Game Over.

The Heart located deep in the Castle. Castle - has Gate. Monsters come out of two tunnels, destroy Gate and then rush to the Heart room to destroy it as well.

In one of the wings of the Castle there are Shop and Black Market areas. Shop provides selection of Weapons, Ammo, Health and Armor items at fixed price.

On the other side of the Castle, there is a Mine and ladder to the roof.

Nota bene:
Project MOON's special actions can't be changed from Quake settings menu.
All new actions added in this mod are available through impulse system. By default, mod assigns to each of these impulses a named alias. Then each alias can be bind to specific button on keyboard or mouse. Most of these bindings are set by default, can be changed by player, but you will have to use config files and/or console.


By default WASD-scheme is assumed

• Q - not used by the mod (KEX / Quake 1 ReRelease assigns Weapon Wheel there)
  
• E - try to Use (see `pm_use` below)
  
• T - print Stats (see `pm_stats` below)
  
• F - try to Buy (see `pm_buy` below)
  
• X - print Inventory (see `pm_inventory` below)
  
• C - print Character info (see `pm_character` below)
  
• V - try to Identify item nearby (see `pm_identify` below)
  
• 1 - try to raise Vitality (see `pm_skill1` below)
  
• 2 - try to raise Strength (see `pm_skill2` below)

ReProject MOON's console commands all prefixed with `pm`. You can always check available aliases (and associated impulse codes in left-most column) by typing
in console. Commands that are reserved for server Host, marked with `pms_`.
Commands that change things for players own view are marked with `pmc_` and available for all connected players.

• `pm_character` - show summary, which includes Hearts HP, Player's Experience progress and carried Gold.
  
• `pm_stats` - show Player's character skils (Strength, Vitality etc) and number of unspent skill points.
  
• `pm_inventory` - show Player's equipment (magic armor and ring), plus status effects (like active drugs)
  
• `pm_identify` - trigger surroundings check for items that have special properties in MOON.
  
• `pm_buy` - trigger surroundings check for anything to sale, and buy it if Gold allows.
  
• `pm_use` - trigger surroundings check for Magical items to wear (magic armors and rings)
  
• `pm_skill1` (`pm_skill2`) - raise character's Vitality (skill1) or Strength (skill2) by 1 point

This mod is resurrection remake of original Project MOON a.k.a Moon Rizing (yes, with Z) created by 3d[Power].

Limited Warranty:
Author expressly disclaims any warranty for any part of this Package.
The Package is provided "as is" without warranty of any kind, either express or implied, including, without limitation, the implied warranties of merchantability, fitness for a particular purpose, or noninfringement.

Responsibilities:
You are entitled to use this Package for personal use, but you are not be entitled to sell or gain profit of it.

(Re-)Distribution:
You may freely transfer this software Package citing original and remake authors and keeping this license and URL of this item.

Source of Power
https://github.com/Sviat/quake_moon