Copied from Ultra Defrag Homepage:


UltraDefrag is powerful Open Source defragmentation tool for Windows NT.
It is very fast, because the defragmenting is done by kernel-mode driver.
They are three interfaces to them: graphical, console and native.
The GUI is very useful, because it represents your filesystem visually as a color coded cluster map. The console is another option for those that prefer the command line. It allows you to run UltraDefrag from the task scheduler and scripts.
Finally, the native executable will run at boot time in a manner similar to chkdsk.

The design of UltraDefrag is very simple.
There are no skins and other unnecessary stuff.
It is a small and powerful program!

It can be used on Windows NT 4.0, Windows 2000, Windows XP, Windows Server 2003, Windows Vista and all of the 64-bit editions of Windows.


UltraDefrag has the following features:


* Defragmentation algorithm was completely rewritten to be more effective.
Now UD is more reliable and effective.

* Very fast defragmentation, the work is done via a kernel mode driver which has an optimal defraging algorithm.

* Single file or directory defragmentation ability.
Select any file or folder in Explorer and choose the appropriate context menu item to defragment them.

* Debug logging feature - Program writes debugging information to %windir%UltraDefraglogs directory. That means if your windows is installed in drive "C" and directory name is "Windows", then logs can be found in C:/Windows/UltraDefrag/Logs.

* Very small engine written in pure C.

* PortableDefrag can be installed on demand which can be carried around in USB storage devices and used without any installation.

* Nice graphical interface - compact and functional.

* Safety, because the file moving is accomplished with Microsoft's own Defrag API.

* Simple to use.

* Set program's filter to exclude unwanted files and folders from the analysis.

* Ability to generate html reports of fragmentation status.

* Ability to include/exclude files based on simple filters.

* Native x64 support.

* Free: Distributed with full source code under the GNU General Public License.

* Many GUI translations were made:
Catalan, Chinese (Simplified), Chinese (Traditional), Japanese, Dutch, French, German, Greek, Italian, Portuguese, Slovak, Slovenian, Czech, Korean, Latvian, Polish, Portuguese (Brazilian), Spanish (AR)

* Scripting support for boot time interface.
Now you can do anything with your drives during the Windows Boot Process.

* Portable Version also available.

* Complete documentation avalable both online and on the installer.


Changelog:


Defragmentation algorithm was completely rewritten to be more effective.

Free space optimization algorithm was completely rewritten to be more effective.

A lot of important bugs were fixed

Console and native programs are much faster now.
Set program's filter to exclude unwanted files and folders from the analysis.


Comments from the uploader (olofolleola4):
Here is the link to the install instructions for Windows Vista: 
http://ultradefrag.sourceforge.net/handbook/installation.html#vista

This package also includes a Portable version of Ultra Defragmenter.
Just open the Start menu-->UltraDefrag-->Portable package.
Then you just copy the files to a Removable drive and you can enjoy the program on a Removable drive. :)