Memory Diag is a nice free utility app available on the Mac App Store. Like a lot of memory utilities (including the OS X Activity Monitor), it will analyze your RAM usage, tell you what applications are using the most resources, and offer to clean things up by purging unused processes.
The app lives on your menu bar, and there are three themes to choose from. The menu bar icon is dynamic and gives you a quick look at how much utilization your RAM is getting. I'm often near the limit, which slows up my Mac and forces OS X to use the hard disk as virtual memory. Memory Diag tells you what things are draining your computer's memory. It's possible to have so much RAM filled that Memory Diag can't optimize, but it will suggest which apps to close. Safari can grab a lot of RAM, along with Photoshop (which I am using almost all day long).
Memory Diag for Mac OS
The app has nice clear menus, and the developer maintains an FAQ on his website. The only thing I would change is to have an actual numerical display of RAM usage in the menu bar. The graphic thermometer is small, and doesn't draw your attention. There were some complaints from a few users that the app itself was claiming 100% CPU time on their Macs. I could not verify this, and every time I checked Memory Diag it was running smoothly and not bogging down my Mac.
Memory Diag is free for a limited time, so grab it if you need some RAM optimization. Memory Diag requires OS X 10.9 or later and a 64 bit processor.
Note: Not everyone agrees these apps solve RAM problems. It is certainly true that whatever cleaning you do will be undone by time as mores apps are opened and closed. As I stated, I had no issues with the apps, and user reviews are generally positive.