DiskTuna (formerly DiskTune) is an on-demand, free, hard drive disk defragmentation and optimization software.
There are no background services, startup or processes to worry about. DiskTuna is only about 1 MB and uses very little memory and runs quickly, in part because of this.
One of its best uses is to use your context menu (right-click) on any drive, file or folder.
DiskTuna offers 3 modes. Defragmentation handles just the basic, quick defragmentation. Optimization can be run every month or two and not only does defragmentation but will also compact and move the most used files to the fastest, most accessible part of the drive. Finally, there is compact which, as just mentioned, packs files together to prevent fragmentation from occurring. This can be used between the Optimization runs.
DiskTuna also can create shortcuts to your frequently used defragmentation and optimization tasks to save time and hassles.