Ah ok, I finally had someone who had the same idea :)
A game called "World Wide Adventure" : http://www.wwajp.com/
Includes : - A user-created world - User-contributed tilesets
With the differences that : - It's not free software, and - It's all in japanesese (thank you google translate ^-^)
Apparently, it's made by the same who made MagicTower. Makes sense.
definitely interesting ! :-) All in Java, too.
neat! – lion