What is "hammerfight"

Hammerfight, previously known as Hammerfall, is a 2-dimensional physics-based video game published by Kranx Productions and 1C for Windows, Mac, Linux and PlayStation Portable. The game was part of the third Humble Indie Bundle. Ryan C. Gordon ported the game and the underlying game engine, "Haaf's Game Engine", to Linux and Mac OS X, and released his port and source code under a free software license.