GameGardens: Free MMOG dev and hosting
From the makers of PuzzlePirates: Game Gardens.
A place to play online multiplayer games and a place for game developers to create their own multiplayer games and host them for others to come and play. If you can program in Java, you can use their multiplayer game toolkit to create your own games, and then upload them to the site for others to play.
Check out their sample games and tutorials.