JkDefrag 4.1 Final

JkDefrag is a free (released under the GNU General Public License) disk defragment and optimize utility for Windows.
Completely automatic and very easy to use, fast, low overhead, with two optimization strategies, and JkDefrag ia able to handle USB disks/sticks and floppies.
Included are a Windows version, a commandline version (for scheduling by the task scheduler or for use from administrator scripts), a screensaver version, a DLL library (for use from programming languages), and versions for 64-bit Windows.
JkDefrag is based on the standard defragmentation API by Microsoft, a system library that is included in Windows 2000, 2003, XP, and Vista.
All defragmenters are based on this API, including commercial defragmenters. JkDefrag is therefore very solid and there is no risk of losing data.
You can stop the program at any time, it will finish the current file in the background.
If your disks use NTFS then youre even safe when the computer crashes in the middle of defragging.
Nevertheless, its still a good idea to backup before defragmenting, just like with other defragmenters, because the heavy use of the harddisk may trigger a hardware fault.