I've tried half a dozen system monitors for macOS and rNitro is the first one that feels like it's actually built for the user, not for collecting data. The CLI has that satisfying btop-style TUI — real-time CPU stats without the bloat, without a background service phoning home, without a subscription paywall.
Setup was a one-liner curl install, checksums included so I could verify what I was running before I ran it. That alone puts it ahead of most "free" utilities in this space.
If you want to actually see what your CPU is doing instead of guessing, this is it.