MemoryKeeper installs a rather large icon in your Mac's menu bar, which, unfortunately, you cannot hide or shrink. It shows you the amount of free memory you have available, which you can also find using the Activity Monitor. Click on the icon to open the app and then click the blue Clean Memory button to initiate a scan.
MemoryKeeper ran for less than a minute on my MacBook Pro, which has 4GB of memory, and freed up 265MB of RAM. I ran a second scan an hour later and it freed up an additional 503MB of memory. I can't say my Mac felt considerably faster after letting MemoryKeeper do its thing -- iPhoto and iTunes continued to operate in their typically lethargic ways, for example -- but my usual multitasking of switching between various browsers and a handful of productivity apps felt perhaps a bit peppier.
After MemoryKeeper finishes scanning and cleaning your Mac's memory, it'll offer to set up its automatic cleanup feature. You can also access this feature in the app's preferences. You can check a box to enable automatic cleanups, and you can set the threshold of free memory available when such a scan is run. You can also choose to run either a Quick or a Full cleanup. According to the app, a Quick cleanup will not affect performance while it runs, whereas a Full cleanup may cause a dip in performance in an effort to provide a deep and complete cleaning.
The logic of running an app in the background in an effort to save memory resources does not agree with me, so I'll likely utilize only MemoryKeeper's manual cleanup feature during times when my MacBook is acting sluggish.
Do you use a memory-cleaning app on your Mac to keep it running smoothly? If so, please share in the comments below.