JkDefrag is a free open source disk defragmenting utility computer program for Windows. It was developed by Jeroen Kessels beginning in 2004 and is released under the GNU General Public License. The "Jk" part of the utility name is taken from the developer's name, Jeroen Kessels. In 2008, from version 4, much changed from previous versions; JkDefrag was renamed MyDefrag by its developer, and JkDefrag was discontinued, although still available. MyDefrag is closed source freeware.