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.
Simply because I've had some negative responses due to Manic Digger having similar texture to 'a certain other game' I decided to show that Manic Digger fully supports custom textures. This was taken from a brief period I spent on one of the German hosted servers.