If you don’t insist on freeware (price is quite reasonable, though, somewhere around $25), there’s also JV-16 Power Tools from Macecraft which is quite safe in its default mode. A few years back (2003?) there was a version in which even the default mode was overly aggressive, but versions before and since are safe enough that you can usually safely bend the rules and not bother with backups.
I used to use Jv16 back in the days when it was still free and it was excellent. It’s named after it’s creator, Juoni Veera, a Finnish guy who was 16 when he first released it. He created Macecraft as a business later on and started charging for his creations. You can still find the last free version of it but it’s only compatible up to XP.
Comodo System Cleaner has a registry cleaner.
Seems not that agressive and offers a lot of backup/recovery strategies.
Also it is standalone (does not require installation).
Yep that one killed my PC 6 months ago >:( and thank GOD! :o for my backup of True Image ;D
Edit: Tech thanks for the screenshot ;D of Comodo Register Cleaner I’ve been chasing around to find what it look like the update version thanks for that Tech.