Here's a massive multi-player zombie experience!
Urban Dead is a free-to-play browser-based multi-player game where you play the survivor or victim of a zombie outbreak in a quarantined city centre, alongside tens of thousands of others.
Here's a screenshot of play.
Here's the low down:
You're a citizen of Malton, a city that's in the process of being evacuated and quarantined to contain a sinister contagion - you play as either a trapped civilian, a member of the evacuating military, a scientist operating in the background, or a victim of the early outbreaks.
Malton is a grid of 100x100 city blocks, each of which is either a nondescript street, or a particular type of building - you move around the map by clicking on the names of the blocks. Buildings can be entered and barricaded by survivors, to shelter from the zombie hordes that roam the city.
Other citizens of Malton appear on the map as names in coloured boxes (the colour matching their class; green for Military, blue for Science, red for Civilian and grey for Zombie); they also appear in the location's description.
Some character classes start with equipment, and all characters can search to find further objects during the course of the game - some are weapons, some are one-use items, others have subtler or more permanent effects. All characters start with at least one Skill, which grants them an extra ability or bonus in the game - by gaining experience points, players can buy further skills and develop their characters.
Players get fifty "actions" per day - these are be used to move, attack, search or otherwise interact with the city. When your action points are gone, you have to wait for them to recharge. (Players remain visible and vulnerable on the map when they're out of Action Points or logged out; survivor players should find secure shelter between logins.)