Hammerfight

Hammerfight is about 2D battles of flying machines equipped with various slashing, piercing and blunt weaponry.
A unique combat style is based on realistic physics simulation, and it ties the movements of the rider to the movement of your mose. As you wave your mouse, your rider swings his warhammer, smashing the foe into the wall!

Minimum system requirements: 

CPU: 2.0 GHz (x86 compatible)
RAM: 256 MB
GPU: OpenGL-compatible with 64 MB VRAM
HDD: ~120 MB