These are the factions availabe in the Star Wars Galaxy mod.

These guys own the galaxy. Death Star, Darth Vader, I is ur father. You get the idea. Because they funnel more funds into their military than anyone else, they have access to the best high-end weaponry. All of the core worlds are dominated by the Empire.

(full title: Alliance to Restore Freedom to the Galaxy)
Made up of a variety of groups, including ex-military personnel, that have been side-lined or stepped-on by the Empire. Essentially a guerrilla effort to pry the galaxy away from Sith control. Their fleet is made up of ships obtained from the free market, raiding military depots, or supplied by allies and converted to military use. They are lacking in large capital ships and weapons, but make up for it in the experience in their pilots and commanders. Their wiley nature is expressed with better thrusters than what the Empire has, giving them an edge in dog-fighting and retreat.
The Alliance has many allied sectors outside of galactic center, and sometimes ends-up near the edge of the galaxy.

This faction is a catch-all for any offensive parties looking to take advantage of the civil war. This includes pirates, underground factions, general ruffians, etc. They use the same blocks as the Alliance, but have more individualized ships (more weapons) and menacing/dirty coloring.
The pirates are scattered all over the place and can pop-up just about anywhere.

After the Clone Wars, Separatist factions retreated and secluded themselves to survive reprisals by the Galactic Alliance. Still relying on their droid armies and technology, these parties now serve their own purposes and are either reaching for power, or seeking to survive by staying hidden. Pretty much the same blocks as the ofther humanoid factions, but they rely on droid fighters (drones). The Seperatists are scattered around the outskirts on the galaxy.

Interlopers from another galaxy intent on expansion. They abhor droid and AI technology, basing all of their tech on the modification of living organisms. They travel in living ships including the World Ship that allows transversing intergalactic distances. Instead of engines, they use Dovin Basal organisms that alter gravitational forces to 'pull' ships forward. Warlike and alien, the Yuuzhan Vong are set to conquer anything in their path. They reside on the very edge of the galaxy.

Based on their cold home world, the Chiss maintain their region with force. Their isolationist mentality means they keep to themselves and intrusion on their territory is not tolerated. Although they do have some contact with elements in the Empire, they have their own independently developed technologies and Star Destroyers. Megamasers, cloaking, and alternative projectile weapons equipped on a hardy defense fleet. The Chiss are located in the outskirts of the galaxy in a single medium-sized region.

A race of dinosaur-like reptiles, the Ssi-ruu reside in the Unknown regions. Their resource-poor home world lead them to develop 'entechment' technology that essentially generates energy but sucking it out of living organisms (people). Although their military is inferior to other races, they can be dangerous. Their Paddle-beams can hit targets almost instantly. They also bulk-out their fleet with droid starfighters. The Ssi-ruuvi are located in the outskirts of the galaxy in a single medium-sized region.

A nomadic warrior race in the Unknown Regions. Their technology is not strong, but they are ruthless. They do not have strong shield tech, but instead house prisoners in shield bubbles on the exterior of their ships, forcing attackers to kill innocents. Expect their weapons to follow the same viciously practical attitude. The Vagaari are scattered around the outskirts of the galaxy.

A colony of various insect races connected by a hive-mind. The Killik colonies are under-equipped with very basic technologies and armor, but make up for their weaknesses with enormous numbers. Their giant Hive Ship houses the colony while their fast Dart Ships handle defense. Individually weak, yet their reproductive capacity can be a serious threat to the rest of the galaxy. The Killik are scattered in small groups around the outskirts of the galaxy.

A fleet of droid battlecruisers created by some unknown race eons ago. The fleet is fast, mysterious, and uses overpowered alien technology. After sitting dormant for millennia, it's on the move and ready to annihilate all life. The Eternal Fleet can only be found in a single small region around the outskirts of the galaxy.

(non-playable)
Scattered from the same galaxy the Yuuzhan Vong originated, they are droid aggregates made up of assembled parts. Their AI's are domineering and aggressive. They have no technology of their own, but rather add to themselves from whatever parts they come across. Large in size - they are dangerous, chaotic, and care only for themselves. The Abimonor are rare and only occupy a couple of small areas around the outskirts of the galaxy.
* This faction is unplayable because they do not have a block-set of their own. Instead, they are a command module connected to a junk-pile of parts from other factions. More of an environmental hazard than a real faction.

The original enemies of the Abominor. They are perfectly-shaped droid life forms that seek symmetry and order. Generally peaceful by nature, they will defend themselves if necessary. The Silentium are rare and only occupy a couple of small areas around the outskirts of the galaxy.