It's a giant monster online fighting game. Originally intended to just be a sequel to the Godzilla fighting games, this time around they are collaborating with the community to implement custom and other licensed monsters.
Personally, this project piqued my interest because they've announced that Cthulhu and the Stay-Puft Marshmallow Man will be playable characters. My mind just explodes with awesomeness when I think of how incredible that battle would be.
Check it out, and stay tuned for an Overgrowth map inspired by the genre.