KJDefrag is a freeware portable disk defragmenter for Windows 2000, XP, 2003 and Vista, both 32-bit and 64-bit. There is no need to install the software nor does it save any configurtion options in a file or the registry allowing you to run it from any portable USB disk drive.

The download package contains three programs-

1) jkdefrag.exe- which is the main executable that needs to be run from any computer
2) jkdefragcmd.exe- command line version of jkdefrag.exe for use with Windows task scheduler
3) jkdefragscreensaver- Runs the defrag as a screensaver

Download Windows 32-bit version here while the 64-bit version can be downloaded here