The timeline is Dungeon of the Endless - the Success, a prison transport, crashes on Auriga.
Endless Legend - the surviving crew and prisoners have formed their own society: the Vaulters
Endless Space: Disharmony - Having escaped from Auriga, the Vaulters have become one of many space faring races/nations. But maybe it is time to go back home, because Auriga holds a lot of knowledge.
Then you have the droid Opbot in every game and various creatures and factions had parallel evolutions on Auriga and the rest of the galaxy. (Necrophages - Cravers, Silics - Harmony, what's their names - Hissho)