UltraDefrag 

Product: UltraDefrag
Website: http://ultradefrag.sourceforge.net
Type: Open Source
Requirements: Windows XP/Vista/7

UltraDefrag speeds up the computer by defragmentation of files.

When files consist of many little fragments scattered around the disk the computer needs more mechanical work to read them. Because of that the disk access becomes slower.

UltraDefrag reduces the file fragmentation, thus it makes disk operations faster. Also the program can optimize a whole disk placing all the files to the fastest part of the disk - to its beginning.

In contrast with the most other disk defragmenters UltraDefrag can defragment locked files by running during the Windows boot. Actually all files including registry hives and page-file can be defragmented there.

Also UltraDefrag aims to be fast, simple, reliable and efficient.