Project EF-12 is a free game engine, which somewhat resembles 3D fighters like Virtua Fighter and Tekken, but there's a twist on this one that's unlike many others, outside of MUGEN.
This particular product is a totally customizable 3D fighting game engine, which can be altered through modifying a series of spreadsheets.
As such, users can change many aspects of the title, from its characters, their abilities, appearances, stages and even stuff like the game's user interface.
In the version that was demoed at the Tokyo Game Show, there was even a character who played like a 2D fighter, despite the being in a 3D game.
If you so choose, you can implement new character models from scratch, and using someone else's modded fighters would be as simple as downloading and extracting some spreadsheet along with the files into a directory.
project ef-12 English preview : youtube.c0m/watch?v=PHE5TK_iG6E
Steam Greenlight : steamcommunity.c0m/sharedfiles/filedetails/?id=196830672