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.
Someone made this rather nifty sign on 'exe creative 5' server... sadly they'd made it on the 'freebuild' side... and it has since been griefed to hell and back. So, unknown sign maker - here it is unspoilt for all to see.
The trollface next to it makes it complete.