"So we have a few great Free Software gaming engines now, like DarkPlaces used in Nexuiz, Cube 2 used in Sauerbraten, Qfusion used in Warsow, soon id Tech 4 which is used in id Software's Quake 4, Doom 3, Enemy Territory: Quake Wars along with many others, and the HPL1 engine used in Frictional Games' "Penumbra: Overture". All of these engines have some combination of normal mapping, bump mapping, and/or parallax mapping..."