Best Mac Cleaner: CleanMyMac X (Free to try, starting from $39.95 to buy) Most newer Mac machines (especially MacBooks) are now with small-volume flash storage starting from 256GB, that means your Mac will fill up quickly and run slowly after some time. What can you do? The answer seems oddly simple: clean up Mac drive.
Why You Should Use an OS X Duplicate File Finder
Duplicates waste your space. If you have never sat down and dedicated time to finding duplicates on your computer, then there really is no way of putting it gently - find time to locate and erase them off your Mac. Deleting duplicates will free up decent space on your computer, though the process can of claiming that space is an incredible pain in the neck (which is probably why you haven’t done it before). There is plenty of guides out there on how you can find duplicates without using a third-party cleaner, but the truth is that it is not worth your time doing it manually.
Save yourself some time and effort — grab MacFly Pro. Launch the application and select Duplicates. Hit ‘Scan’ and let MacFly Pro do the searching. Once done, hit ‘Review Files’ to choose the ones you want removed. Finally, click ‘Delete Selected’, to remove the files.
App Cleaner OS X Recommendations to Deleting Apps
If you want to keep your Mac clean, then do it a favor and stay on top of your apps library. It is simple, apps usually run background processes, build cache, check for updates etc — all of these processes use your computer’s resources.
“I want unneeded apps taking up my storage and RAM.” said no one ever.
Remove Apps and Installation Files You Don’t Use
To remove an app, open Finder>Applications. Simply drag-and-drop to Trash the apps you want to delete.
Open Downloads folder (if you have not changed the default path for your downloads) on your Mac and look for dmg files. Those are the files that you use to initially install an application on your computer. There is no reason to keep dmgs after the apps were installed, especially as they can take substantial space on your disk. Select and remove them if you haven’t yet.
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.
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.
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