System monitors

Activity Monitor shows what your Mac is doing, but only while its window is open. A system monitor keeps CPU, memory, GPU, disk, network and sometimes temperature and power readings in view, in the menu bar, on the desktop or in a compact window.

Check which readings each app supports on your hardware, since sensors and GPU data differ between Apple silicon and Intel Macs. Also consider how often it refreshes, how much it uses itself, and whether it lists the processes behind a spike as well as the totals.