Manic Digger is an open-source implementation of block-building games as made famous by Minecraft. Manic Digger aims to be a generic platform ontop of which you can create your own game-types and scenerios. Through server-side scripting, any type of block-building game should be possible.
Manic Digger Binary version (2013-02-06). Recommended when you plan to host a server or prefer a .zip file instead of an installer.