Ultima Online, EverQuest, or maybe even Meridian 59. You're correct of course, but there's another title that released in 1997 that's still going today.
That title is Tibia, and the 2-D fantasy game from CipSoft GmbH has just announced a world-changing summer update. World quests are "highly complex missions which can only be accomplished if dozens or even hundreds of Tibia players cooperate," according to a new press release.
The new quests add another level to Tibia's conflict-driven dynamic that sees players and guilds war with one another for years at a time, as the battlefield will now extend further into the open world and likely result in competition for quest objectives. Tibia is also offering a new quest line for newbs. The comprehensive tutorial series leads new players through various gameplay tasks and offers a concise yet thorough introduction to one of the genre's longest-running titles.