Omega
Originally an asteroid rich in element zero, Omega was briefly mined by the Protheans, who eventually abandoned it due to its thick, impenetrable crust. Thousands of years later, nature did what even the Protheans could not: a collision with another asteroid broke Omega in half, exposing its trove of element zero for easy mining.
A rush ensued as corporations and private individuals tried to strike it rich on Omega, and thieves and outlaws followed in their wake. As space became tight, construction of processing facilities extended vertically from the asteroid, creating Omega's jellyfish-like silhouette. To prevent future collisions, the station is ringed with enormous mass-effect field generators that redirect incoming debris.
Today, Omega is a major hub of narcotics, weapons, and eezo trafficking without even a pretense of civilian government or military control. Only mercenary groups have been able to instill a limited order; the most ruthless is an asari syndicate run by the notorious Aria T'Loak.
