iStat Menus - "An advanced Mac system monitor for your menubar."
Process Explorer - The top window always shows a list of the currently active processes, including the names of their owning accounts, whereas the information displayed in the bottom window depends on the mode that Process Explorer is in: if it is in handle mode you'l…
TaskExplorer - Explore all the tasks (processes) running on your Mac with TaskExplorer.
MenuMeters for El Capitan - MenuMeters for OS X El Capitan 10.11 (and later)
MiTeC Task Manager Deluxe - MiTeC
iGlance - macOS system monitor for the status bar