Ashampoo Magical Defrag
Full user review
"Keeps disk defragged without slowing PC"
Program works in background and pauses when the CPU is active, so it doesn't interrupt or slow PC. HD stays degragmented. I periodically run a separate defrag program and it finds almost no fragmentation to slow down my PC.
None - works right all the time!
Beats any other defrag program for keeping things clean without user input. Great if you are tech support for friends and family (that is- uncompensated).