UltraDefrag is a free and open source disk defragmentation software that helps optimize the performance of hard drives. It offers boot time defragmentation, which means that it can defragment system files that are normally locked during normal operation. The software also includes a graphical user interface, command line interface, and the ability to defragment individual files or folders. Additionally, UltraDefrag has the option to exclude certain files or folders from the defragmentation process.