btop

btop proves terminal apps can be beautiful: real-time graphs for everything, a filterable process tree with kill/signal actions, full mouse support, themes, and GPU monitoring for NVIDIA, AMD, and Intel in recent versions. It launches instantly over SSH, making it the tool for checking on servers and remote boxes as well as your desktop.

Being terminal-based is the only barrier — if you never open a terminal, Mission Center serves the same need graphically. Configuration lives in a config file plus an in-app menu, and GPU stats require the relevant drivers/libraries to be present. There’s essentially nothing else to criticize; it’s a modern classic.