Mac: Your Mac likes to cache things in your "free" RAM so if you need them later you can load them quickly. if you need to free up a lot of memory for a particular task you might not want it filled with cache files. Memory Clean clears that RAM out with a couple of clicks.
Memory Clean lives up in your Mac's menu bar and shows you memory statistics whenever you want them. If you find your RAM is filling up and things are running a bit slowly, just choose "Clean Memory" and it will free up inactive memory that you could be using for other tasks. The app also lets you set a low memory threshold which can trigger an alert or an automatic wipe of the free memory.
If you don't have a newer model with lots of RAM you ought to give it a shot. It's free, after all — though it does enjoy advertising the developer's other apps from time to time.
Memory Clean (Free) [Mac App Store]