The Endless Universe is the name for the loosely connected theme linking three games. Some factions, races, planets and technologies re-appear in the different games.
- Endless Space is a Science Fiction themed 4x game.
- Endless Legend is a Fantasy themed 4x game.
- Dungeon of the Endless is a Tower Defense/Roguelike style game. http://endlessspace.wikia.com/wiki/Dungeon_of_the_Endless
Some more infomationn on the other games can be found on the Endless Space wikia.
A longer background/origin story for the universe can be found on the Aplitude Studios forum in this post.