Windows only: Freeware defrag utility MyDefrag not only handles the basic drive defragmentation tasks, it also includes a powerful scripting engine, a screensaver and a command-line version.
MyDefrag is based on the previously mentioned JkDefrag utility, but there's no regular options dialog for MyDefrag—instead, a set of included scripts handles a variety of defrag tasks immediately, but can be customised to perform much more advanced tasks. For instance, if you wanted to move all your music files to the fastest part of the disk, you can do so easily with a simple script—it's probably not the best choice for the less tech-savvy reader, but the powerful command-line scripting options are very welcome.
MyDefrag is a free download for Windows only. For more, check out the five best Windows maintenance tools.