What is MUGEN?
MUGEN is a highly customizable 2D fighting game engine created by Elecbyte. If you're willing to look, you can find characters, backgrounds, screenpacks, etc. from almost any 2D game ever released, in addition to completely original works. Please note though, that MUGEN is still only a public beta, so there are likely to be bugs and incompatility issues depending on the version you own. There are versions of MUGEN that run under Dos, Linux, and Windows. Give it a shot; you might like it. Besides, it's free! ;)