The final part in my unofficial 3 part series of free, open source must-have utilities. Windows Defrag is incapable of handling large (2GB+) single files, such as ISO files, virtual machine files, etc. can easily be 5GB+ each. At $200, Diskeeper Professional does the best job at this, yet Defraggler is a great free alternative. Defraggler can replace Windows Defrag during installation. While I do not choose this option, I plainly use the portable version to manually defrag at night once a month.