A collaborative, multi-author, Gygaxian-Democracy fueled consensual nightmare.
The idea is to use freely available software, or at least formats to collaboratively work on a sprawling complex of treasure-, monster-, and trap-filled rooms wherein adventurers can go to get rich or die tryin'.
So, like you could take the base map and some room descriptions, fork the thing, and make it your own. Erase a few rooms, start a level from scratch, whatever you like.
Everybody's welcome to jump on board, but I'd sort of like a base to work from that's cool so if you make major changes then make a fork of your own and share your version, too.