UltraDefrag is a powerful, open source defragmentation tool for Windows. It´s engine is very fast, because it is created as a kernel-mode driver.
There are three interfaces to them: graphical, console and native. The first is very useful, because it uses cluster map visualization. Console is good for task scheduler, and native tool – for advanced users and programmers.
UltraDefrag´s design is very ergonomic: no skins, no localization, no animation and so on. It´s a truely small and powerful program!
It can be used on Windows 2000, Windows XP, Windows Server 2003 and Windows Vista. NT 4.0 support is currently unavailable.