Q3A is Quake III Arena in short. OpenArena is a free game derivated from Quake 3 Arena. You don't need Q3A to play OpenArena. Many mods created for Q3A work also in OpenArena. For more info, please read: * /Quake III Arena * /Team Arena * /PointRelease * /Quake Live * /ioquake3 * /Quake III Revolution * List pages beginning with "Q3A/"