Disney's Toontown Online, usually known as simply Toontown and stylized as ToonTown, was one of the first kid-oriented MMORPG games. It lasted from 2003 to 2013 until being closed on September 19, 2013 in honor of Club Penguin. Disney's version of the game itself is considered lost, however a user on Reddit has been able to briefly go into part of the server.
Toontown is/was (depends how you look at it) a game where you play as a cartoonized Mickey-style animal of which you can customize and name. You used pies, squirt guns, falling anvils, and things along that line (a.k.a 'Gags') to defeat robot businessmen named Cogs who were trying to turn the silly and colorful Toontown into a bland and boring business world. (Sound familiar anyone?)
Disney characters and, of course, a premium membership plan were featured until fans took over development of the game.
Toontown picked up a strong community in the 10 years it was run by Disney. Many of these fans are trying very hard to recreate the game. The most popular one is Toontown Rewritten. Toontown Infinite leaked their source code, leading to over 30 other 'private servers' being announced and canned.