Pufferpanel!

OGP is a game server control panel. It uses a web interface (PHP/MySQL) that controls an agent (Perl) running on the servers hosting your games. It is used to start/stop/monitor game server instances. More features like a config file editor are coming soon.

GameCP: game & voice server hosting control panel - create, manage and control game, voice or radio servers. Linux, Windows & FreeBSD Compatibility

Bright Game Panel is a free and open source game server control panel. "BGPanel" utilizes many standard technologies available on many shared hosting platforms which gives all communities the ability to remotely control their game servers.

Multicraft is a Minecraft multi-server management solution running thousands of servers.

Bukkit Webby is a lightweight web administration that is easy and fast to setup It's made of two components :

SpaceBukkit is an advanced and completely free open-source administration panel for bukkit servers. It will make all those repetitive tasks like player and plugin management, backups and server tasks fun and easy, so you can start playing minecraft again.