Chat and fight is a multiplayer game in webgl. it is very hackable. other people can easily do their own world.
see homepage for more details.
git clone git@github.com:jeromeetienne/mmo3d.git
cd mmo3d
make server
cp -a public/montain public/foobar
use your text editor in public/foobar :)
point your browser here
you do that whereever you want. Personnaly i go for nodejitsu, they got free hosting for opensource.
make deploy