Ehh, sorry to revive such an old thread, but I have some contributions.
M.U.G.E.N. One popular example is Marvel VS Capcom 3, the unofficial. Actually there is several different versions.
The download place I got it from was no longer there but fear not you can probably find it everywhere to download. To my knowledge MUGEN is absolutely free and legal where allowed.
VIDS To highlight the occasion:
Popular YT vid:
Looks like something that would actually be released--err the title of it anyways.
Also, no downloads necessary
, you can play some flash games and even hacks of old games online at www.derok.net
and I'm just going to leave it at that.
Have a mac? Like old RPG's? Try Odyssey:Legend of Nemesis
! Also I have discovered some stuff NOT COVERED IN THE WALKTHROUGH! So if you have questions and you are playing this, drop me a line! It's free!