iStatistica Pro is an advanced system monitor for macOS.
Overview your battery statistics, realtime informations about CPU, RAM usage and much more. Network statistics includes external, gateway and local IPs, speed and data rates chart.
Additionally, I also like "MEMORY" panel. it shows more information than other apps.
One key point needs to be improved:
Opening a normal window will trigger a high CPU usage.
It's a beautiful app, and I think it's the ONLY one app which can show powerful detail information on Today Widget.