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.
Memory Clean is an app for optimizing your Mac's memory and is best used after you have finished using a memory (RAM) intensive app or game. It replicates the feeling of a fresh system restart. Memory Clean works by purging the Mac's inactive memory and is best used when you close an intensive program that you do not plan to use again quickly. Memory Clean works by purging the Mac's inactive memory and is best used when you close an intensive program that you do not plan to use again quickly within a few hours. Controlled Cleaning With Memory Clean, you can set the app to automatically clean your memory when free memory falls below a defined threshold amount. Memory Clean is an app for cleaning up your Mac OS X device memory at intervals. Memory Clean is available from the App Store or several download sites, and installs easily. Memory Clean is a free.
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.
Ram Cleaning App Mac Download
CCleaner beta is out for OS X, used on PC's and combines cleaning and scrubbing of the drive if setup correctly.
Free Mac Cleaning App
If your interested in performance, read my post here