If you have ever played Quake III probably know how addictive it gets when played online or even when played with computer bots, Open Arena is a MOD (modificaiton) of Quake III engine and this Mod is completely free and portable so that you can play it off your USB stick where ever, when ever even with an ancient video cards on laptops or desktops alike.
All the system requirements both for CPU and GPU are equivalent to Quake 3, its a cool game, runs from your usb stick with atleast 75 MB free space, or you can unzip its rar file and save it somewhere on the disk to play from.

Download
http://rapidshare.com/files/149878813/oparpo.rar

NOTE:  This link may die few days later, so grab it now, i would not probably able to update the link once its dead, because its not uploaded by me if you got it before its dead then Happy Shooting!