CCleaner

Optimization and Cleaning
CCleanerIf your PC is running slowly then try CCleaner. It is the number-one tool for cleaning and streamlining your Windows PC. Using it protects your privacy online and makes your computer faster and more secure. Easy to use and a small, fast download.
This useful utility can cleanse temporary or potentially unwanted files left behind by a variety of different applications along with browsing history, recycle bin contents, internet cookies,  file fragments, log files, memory dumps,system caches  and a whole host of other data.

CCleaner also has an integrated registry cleaner to seek and destroy problems within the Windows registry. It gives other options for alteration of programmes installed on your computer as well as start-up configurations.

CCleaner for Mac OS
CCleaner for Windows PC