M.U.G.E.N is a 2D fighting game engine designed by Elecbyte starting in 1999. Elecbyte distributed beta versions that ran under DOS, Linux, and Windows. The engine allows for anyone to create characters, stages, and other game objects through interpreted text files and graphics and sound compilations, and it also supports MP3 background music during gameplay. The engine is very powerful and flexible, allowing for the same type of functionality found in most any commercial 2D fighting game, such as the Street Fighter games produced by Capcom or the King of Fighters games produced by SNK.
My husband was playing around online and found M.U.G.E.N and is in the process of downloading it, don't worry it is legite to download. I have messed aroung with the engine a bit and it is pretty cool. Like all computer games you can customize the controls to your liking and you can make up your own moves, characters, and fighting style, pretty sweet huh. So far we have a couple of DBZ characters started on MUGEN. I can't wait to actually play it and see what it can do.