OpenMortal is a free and open-source clone of Midway's classic fighter game "Mortal Kombat", the gameplay and graphics are quite similar to Mortal Kombat with a huge selection of characters to choose from. OpenMortal also allows you to design your own character for the game.
Mac OS X 10.3.9 or newer
Intel or PowerPC powered Mac
Free download at apocalypse.rulez.org