LauraM sez, "Urban Dead is a growing popular browser-based MMRPG (Massive Multiplayer RPG) in which you start off as a human (scientist, military, or civilian) or a zombie in a large city that has become overrun by zombies. When one dies as a human, he turns into a zombie, and zombies can be revived by scientists back into humans. Characters advance by hurting/helping fellow players, looting, doing graffiti, etc.
"It's fascinating the way the game plays in real time. Players are alloted a certain number of action points during the day, but if action points run low, the player had better find a heavily barricaded building so zombie players won't get to him during the night!"
(Thanks, LauraM!)
