Reddit mentions of Steampunk Crescendo - Hardcover

316 has the most elegant combat system I have seen. If I was going to play a game that was only combat, that would be the one I would choose.

Shadow of Yesterday has an interesting approach. It uses the same mechanic it uses for skills. You roll one time against a target number or another character. Except, after the resolution is determined, the players have an option to "Bring Down the Pain" and do an extended conflict that works very similar to combat in FATE. So, if it is a throw away fight or the PCs don't care if they win or lose, they can roll, accept the consequences and move on with the story. If it matters to them, they can risk losing even worse for the possibility of a big payoff. A lot of games talk about the ability for a small fry to beat a seasoned veteran, this is one of the few games that deliver.

Firefly has a system where you take conditions and the character is knocked out of the conflict when the condition reaches its max value.

<shameless self promotion>My game (Steampunk Crescendo) has a mechanic where you roll three dice and after seeing the values rolled, you assign one to attack, defense and achieving your goal. The conflict ends when either your attack dice took your opposition out of the game or the achieving your goal dice exceeded your target. Both sides do this simultaneously, so it is pretty fun to see all four numbers (two attacks and two achievement totals) racing to the finish line.</shameless self promotion>

Those are the ones I find cool and different.