http://davesmapper.com/Link found on
Grognardia.
I believe that this was born out of a set of different projects being shared amongst the
Old School Renaissance and "megadungeon" blogging fans, who have been building up a huge resource of geomorphic tiles - (black and white 10x10 squares with two exits on each side).
Dave's Mapper incorporates tiles created by many different people.
It's fun.