Wikipedia
UltraDefrag
UltraDefrag is an open-source disk defragmenting utility for Microsoft Windows. It is released under the GNU General Public License. The only other Windows-based defragmentation utility with a GNU GPL was JkDefrag, but its GPL version was discontinued in 2008.
UltraDefrag uses Microsoft's defragmentation API and works on Windows NT, 2000, XP, Server 2003, Vista, 7 and 8 operating systems. It supports FAT12, FAT16, FAT32, exFAT, and NTFS file systems.