One lightweight and simple option worth checking out isVitalSigns.
It is, however, only compatible with OS X El Capitan.
it’s possible for you to also set it to display in Celsius or Fahrenheit.
The next tab will display the speed at which your fans are running.
And finally, the last tab displays a RAM monitor.
The stats won’t, however, show up of their own accord.
You’re going to have to activate them.
you could do this by going toSystem Preferences > Extensions.
Here you’ll find VitalSigns listed and just double-check that the menu item “Today” is checked.
Now when you go to your Notification Center, you’ll see the stats you selected listed.
