Clipy offers three essential features for a clipboard manager that I'm using everyday: keep history records of clipboard, quick choose and paste from a pop-up menu, and convert clipboard content into plain text with single modifier key. Of course there are lots of clipboard manager applications available on MAS that can do this and even more, but Clipy better fits my needs.
First, it's *NOT* an MAS application, which mean that it needs not to obey Apple's sandboxing policy. It can interact to system events without the requirement of a separate "helper" utility, thus mitigate the operation overhead.
Second, the resource requirement of this application is extremely low. After one day heavy usage and it only allocated 7MB of memory. Meanwhile, the trusty Pastebot would occupy 50MB+ of memory.
Third, it can operate in invisible mode, hiding both Dock and Menu bar icon.
And last, but not least, it's free.