If you guys like custom, fan-made versions of old hits, that uses reworked versions of original game engine (like reverse engineering of RTTS), there`s a game that perfectly fits for this description.
If you played Dungeon Master as a kids, you`ll like this fan-made game based on its (warped) engine:
http://www.cyberskald.com/conflux/
There are a lot of games based on it`s (reverse engineered) engine of Dungeon Master, but this is definitely the best one.
Not only the game engine is heavily changed (comparing to the original), but this guy also designed it`s own graphic, dungeons, adventures, gameplay and other stuff on a self-made editor.