Urban Dead is a Free To Play HTML/text-based massively multiplayer online role-playing game created by Kevan Davis. Set in a quarantined region of the fictional city of Malton, it deals with the aftermath of a zombie outbreak. Players enter the game either as a survivor or a zombie, each with different abilities and limitations. Survivors become zombies when they are killed, while zombies can be "revivified" with appropriate technology, returning to life as a survivor - any character played for long will thus spend some time alive and some as a zombie. There are no non-player characters in the game: all survivors and zombies are controlled by players.
Urban Dead went live in July 2005.
Source: Wikipedia, "Urban Dead", available under the CC-BY-SA License.