Including the famous Shoryuken, Hedgewars is a freeware game modeled after Worms. It contains a vararity of weapons and two martial arts skill for each skinnable hedgehog. http://www.hedgewars.org/about.html
A game can get hellish really quick in a server game, but you can play against a com, but if you are new to the game, it's gonna be tough.
Right-Click to bring up the weapons menu, or alternatively, cycle through F1-F9 for each.
- Left and Right moves the Hedgehog in that direction.
- Spacebar to fire your current weapon.
- Backspace to do a backwards double jump.
- Enter for jumping.
Below is the game (and the trailer) in action: