Recently I'm using some very CPU intensive programs on the mac, like Xamarin (Visual Studio), Android Studio and test code.
Sometime, when I'm running a lot of this stuff, the Mac is clearly slowed down and can be useful to know what is going on.
So I did look around for some monitor application, possibly capable to show what is going on on the tray.
I did found many apps but I wanted something small and possible free :)
I did found MenuMeters, a very small and nice app, but unfortunately is not supported since 2014 and thus is not working on the latest releases of Mac OS.
However somebody did write a patch to allow this utility to run also on newer systems (at least for now, it seems Apple is locking down even more the systems to prevent this kind of third party utility to run).
Click here to find the patch for the MenuMeters app.