iStat Menus - "An advanced Mac system monitor for your menubar."
Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
iStatistica Pro - System monitor. Reinvented. 💻 🖥
AppDynamics - Get real-time insight from your apps using Application Performance Management—how they’re being used, how they’re performing, where they need help.
Stats - Simple macOS system monitor in your menu bar.
Zabbix - Track, record, alert and visualize performance and availability of IT resources