Aspyr has released a free demo of its Mac OS X port of id Software's Quake 4.

The game runs natively on both PowerPC- and Intel-based Macintosh computers. Gamers take the role of Matthew Kane, a member of the legendary Rhino Squad, on a series of heroic missions to destroy a barbaric alien race.

The demo offers the first part of the single player game, in which players must fight to clear a landing zone for an invasion force.

It's no lightweight download - the demo weighs in at 536MB. You can download it here.