M.U.G.E.N.

M.U.G.E.N is a 2D fighting game engine that is enables you to create commercial-quality fighting games. Almost everything can be customized, from individual characters to stages, as well as the look and feel of the game. Customizable title screen, character select screen, life and bars, game sound effects, fonts and more. Characters can have any number of sounds and sprites of any size limited by your computer's memory.