FASA published such games as BattleTech, Shadowrun, Earthdawn, Crimson Skies, and Vor. Their games didn't have a core underlying set of rules as other publishers sometimes do (such as White Wolf Game Studios' Storyteller system, or Steve Jackson Games' GURPS system.)

Sadly, FASA is no more. They've closed their doors. Earthdawn was sold to Living Room Games a couple years back, and Shadowrun is now owned by WizKids LLC. Let's hope good things continue to come out of those game lines.