Alien Arena 3

Alien Arena 2007 is a Free online FPS first person shooter game that takes a few of the best aspects featured in such popular games as Quake III and Unreal Tournament and then further combines them with unique and original ideas. Based on a retro style Alien theme, Alien Arena 2007 is not only fun to play, it also contains that old school element that you just don't find in most modern Deathmatch style games.
How to Run Alien Arena Portably:
* Install the software to the default path. Typically C:\Alien Arena 2007
* Copy the "Alien Arena 2007" folder to your portable USB device.
* Delete unins000.dat and unins000.exe from the copied folder
* Launch the game by running crx.exe
* Now, you can uninstall the game from your PC and run it entirely from the portable USB device.
Source: http://www.pendriveapps.com/