UO on a free shard. I spent so many hours on that. Honestly I don't remember 'playing' it that much. Most of the time I just logged in and chatted. It was a small shard but we were all very close. In fact it was my first boyfriend that introduced me to it and then once we'd split up 4 years later I met my second boyfriend on there! There was a huge age range on there, from teens to someone in their 70s. Only 2 of us were tamers so we ruled the market there and I had some uniquely hued mares and dragons that the other tamer, Lord Crow, had tamed for me during an event. Power scrolls weren't needed and you could train up all skills but there was no accelerated gain. I remember spending 16 hours one day to go from 90 - 100 mining. I have no clue why but I tamed a walrus and called it Chrystan, after the shard owner, and would turn up with it to the weekly events just to wind him up. I've continued that tradition on and Pevil now always has a tamed walrus in her stable. Sadly that shard disappeared sometime around 2006 I think. I've continued on and off on OSI but it just doesn't feel right. UOAlive however is starting to feel like home now.
UO started a big MMO addiction though. EQ2, WoW, Guild Wars (though I don't class that as a 'true' MMO with the instanced hubs and quest areas for just your party), Guild Wars 2, Silk Road Online, various tiny ones no one has ever heard of and I don't remember, Istaria (formerly known as Horizons and one I still play), FFXIV, ESO, New World, LotRO, Age of Conan, Vanguard... I'm sure I'm missing a load off the list.