I listed the alternatives already. They're all built in.
CCleaner's registry cleaner is the main issue (aside from the fact it makes computers literally slower by clearing every single cache it can find). Some of the issues it has caused:
- Registry damage: Windows 8 store was damaged/corrupted by a previous version (you had to run DISM to repair it), Windows uninstaller corruption (this impacted Mcafee anti-virus around 2009, the uninstaller would become unusable), deletes preferences for unconnected devices (USB sticks, external drives, network drives, etc) so if you have any software installed externally the drive letter may shift and the software will break, deletes unmounted but valid COM objects, and so on...
- Damage: http://features.en.softonic.com/the-dangers-of-using-ccleane....
- Article: https://bitsum.com/regcleanerfacts.php
- Wikipedia: https://en.wikipedia.org/wiki/Registry_cleaner
- Microsoft support article ("serious issues can occur when you modify the registry incorrectly using these types of utilities"): https://support2.microsoft.com/kb/2563254
- Microsoft Article: http://windows.microsoft.com/en-us/windows/are-registry-clea...
Everyone is saying the same thing. Registry Cleaning is unnecessary, won't improve performance, and really only offers you a chance of doing damage. Registry cleaning hasn't been important since XP, and XP shipped over ten years ago.
Everyone else CCleaner does is either stupid (clearing caches) or duplicated of internal functionality (IE cache clearing, Recycling Bin emptying, etc). Plus Disk Cleanup isn't a new addition to Windows.