JkDefrag is a disk defragmenter and optimizer for Windows 2000/2003/XP/Vista/X64. Completely automatic and very easy to use, fast, low overhead, with several optimization strategies, and can handle floppies, USB disks, memory sticks, and anything else that looks like a disk to Windows. 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), versions for Windows X64, and the complete sources.

JkDefrag v3.33 (December 23, 2007)
- Fixed a bug in the Windows version that for some users caused the display of the diskmap to get stuck.
- Fixed a bug in the forced-fill optimization that caused the program to skip fragments that were left by filling a gap with a part of the fragment.
- If the volumename of a disk cannot be determined then the program will now fallback to using the mountpoint of a volume to open a handle.
- If the user specifies a short input mask without a wildcard, for example "C:" or "C:\", then the input mask is rewritten as "C:\*".
- Fixed a bug where the special "DisableDefaults" spacehogs mask only disabled the masks, but not the "Files bigger than 50 megabytes"" and "Files not accessed in the last month" criteria.
- Bundled some language-specific SpaceHogs masks into "?:\\*\\Installshield Installation Information\\*".
- Moved the "Volume ID" message for FAT disks from debug level zero to 6.