from wiki: M.u.g.e.n or commmonly known as mugen is a freeware 2D fighting pc game.
M.U.G.E.N - Wikipedia, the free encyclopedia

Developers create video game characters and produce them onto this engine. They also recreate popular video game fighting characters.

Mugen Demonstration
YouTube - Mugen- Matrix Revolutions

It is quite a popular mod-driven community, apparently people have made over 1000 characters from original fighters, comic book characters, parody characters, etc.

I'd like to make a request to the Wii programming community to make this playable on the Wii. Anyone daring to try?
User Glezx Needs your help!
User:Glezx/WiiMUGEN - WiiBrew