Stats - Simple macOS system monitor in your menu bar.
iStat Menus - "An advanced Mac system monitor for your menubar."
Fanny - Monitor your Mac's fan speed and CPU/GPU temperature from your Notification Center.
iGlance - macOS system monitor for the status bar
RunCat - This cat runs at the speed according to the CPU usage of your Mac. By looking at its running, you can see how much your CPU load is.
CrystalCPUID - CrystalCPUID is a CPU utility software. Key Features: Support AMD64/EM64T