Anarchy Online

Anarchy Online came out in 2001 from Funcom and was the first sci-fi MMO to really commit to a future setting. The world was Rubi-Ka, a corporate-run planet locked in a civil war between the Omni-Tek corporation and the rebel Clans, with a third neutral faction caught in the middle. Character builds were absurdly deep, you could mess around with implants, nanos, and skill points to make some genuinely broken combinations. The launch in 2001 was famously catastrophic, one of the worst MMO launches ever, but Funcom kept patching and rebuilding it, and the game went free-to-play in 2004 and just kept going. Its still running today with active players, which is honestly amazing for a game that almost killed its own studio at launch.