TuxScape

An open 3D world built in the shape of the old browser MMOs: your stats sit in the window title, presents and pots break open for health drops, and the enemies are ordered so that you can tell which fight you are ready for. Zombies, green flies, baby dragons, skulls and whirlwinds first.

There is no account and no server — the world is yours alone, which is an unusual thing for a game that looks like this.