Mac's don't need defragging as OS X automatically writes 2Gb or below sized files to one contiguous space on the drive. There are certain cases where's it's needed to free up a large spaces on the drive, but not something everyone has to do.
- Free up your Mac’s Storage with these Disk Cleaner Apps for macOS It might be hard to believe but Macs also need disc cleanup once in a while. Using the above mentioned tools you can get rid of unwanted, duplicate, residual, and junk files on your Mac.
- Disk Cleaner is fully customizable! Not only does it scan for temporary and unneeded files, but it can do a deep scan for all large files over 100MB (customizable to any size). You can easily view and remove large files you might have forgotten about and no longer need.
List of Best Disk Cleaning Apps for Mac 1. Disk Doctor Pro. App Cleaner & Uninstaller. Disk Cleaner Movavi. Disk Cleaner. CleanMyMac 3. Duplicate Finder. Download this app from Microsoft Store for Windows 10. See screenshots, read the latest customer reviews, and compare ratings for Total PC Cleaner - Free Disk Space Clean Up, Optimize Memory & Windows System. An old Mac system can store nearly gigabytes of files that are junk as well as unnecessary. All these junk files can be removed with the help of a good cleaner for Mac PC. Here are some of the best Mac hard disk cleaning apps that will save money by avoiding an external hard drive and avoid the laborious task to clean up Mac manually.
Apple Disk Cleaner
Far as other Mac maintainence, there really isn't any except to backup one's files regularly. Keeping Software Updated and run a web browser check to make sure the plug-ins are current.
For Safari and Flash, this check is more accurate
Most of those cleaning programs are junk, especially MacKeeper.
If your friend got onto your computer and visited a bunch of adult sites, then I would recommend something like OnyX, doing ALL the cleaning and maintenance aspects and rebooting, perhaps followed by a Disk Utility Erase free space.
Disk Clean Mac App
CCleaner beta is out for OS X, used on PC's and combines cleaning and scrubbing of the drive if setup correctly.
If your interested in performance, read my post here