Defraggler is a free Disk defragmentation software which lets you quickly defrag the individual files you want to, without having to process the whole drive. The new version now lets you even defrag system files at boot-time.
This compact and portable Windows application supports NTFS and FAT32 file systems.
Defraggler v 2.0 pushes the capabilities of Defraggler far beyond any other free defragmentation tool, by offering complete offline defrag during the boot process with full OS support.
Additionally the UI has been improved with a new Drive Map and customizations. They have also re-architectured the internal defrag processes to make it faster and more efficient!
You can now also defrag system files at boot-time.
To do so, open Settings > Options > Defrag tab > Check run boot-time defrag of system files.
Defraggler v 2.0 beta has been released and can be downloaded from here.
Home page : Defraggler.
You might also want to check out some of the best free defragmentation software for Windows 7.