Advanced System Care
CCleaner
Eusing Free Registry Cleaner
Glary Utilities
jv16 PowerTools
System Mechanic
TuneUp Utilities
Win Utilities
Wise Registry Cleaner
Other (please mention below)
I played manually, deleting registry keys...
Also i used to use Advanced Uninstaller Pro to revert back to older registry & used its Registry Cleaner. But playing with registry is always risky and twice it failed on me.
Luckily I had W98 as 2nd OS and was able to backup my data...