Meridian 59

Meridian 59 has the distinction of being basically the first commercial 3D MMO, launching in 1996 even before Ultima Online. It was simple, the graphics were rough even for the time, but it had everything that would later become MMO standard, persistent worlds, player vs player combat, guilds, and a real economy. 3DO published it, then dropped it, then it bounced through a few different owners over the years. The wild thing is its still around. There are multiple servers running today, both official and fan-operated, and it has a small but extremely dedicated community that has kept it alive for nearly thirty years. Its basically a living museum piece you can still walk around in.