Quarantine is a free open source plugin for Craftbukkit.
It allows admins to create "quarantine zones", in which hostile mobs circulate, and attack players, who have to fight for their survival.
The players can buy items (and enchantments), or sell some, through a local economy system.
Admins can locks doors, which will require players to buy keys to open them.
This plugin is highly customizable, from the starting kit, to the size of the zones.
WorldGuard is required for this plugin to work, as it is throught it's API that regions are defined, protected and saved.
Inventory, location, health, money and score are saved, so a player can resume playing at any time. Pre-game health is also saved for post-game.
Leaderboards require a Redis database to work.