M.U.G.E.N is a freeware 2D fighting game engine designed by Elecbyte. Content is created by the community, and thousands of fighters, both original and from popular fiction, have been created. It is written in C and originally used the Allegro library. The latest versions of the engine use the SDL library.

M.U.G.E.N has gained infamy over the years, in part due to the abundance of 18+ edits and NSFW-centric characters like Kuromaru and Minotaur being associated with the game, to the point that communities have formed around this aspect of it.