UltimateDefrag is a free disk defragmenting utility for Windows. While defrag utilities are a dime a dozen (cheaper actually, since there are plenty of good free programs). UltimateDefrag sets itself apart from the crowd by letting you give priority to the files and applications that you use the most. Essentially, what that means is UltimateDefrag will move the chunks of data you need the most to the highest priority portions of your hard disk.
While UltimateDefrag's "high priority" feature won't make your programs run any faster, you may notice that programs launch a bit more quickly.
You can choose from several different methods for defragmenting your hard disk. You can process fragmented files only, consolidate your directories so that they're all next to one another on you hard drive, order files and folders by name, organize your disc by the most recently used data, or select the auto feature to let UltimateDefrag decide what's best for your PC.
[via gHacks]
Windows has a built-in defragmenter, and while there is nothing wrong with it, it is lacking in a few areas. For example, it cannot defragment the swap file. 
