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.
Process Explorer - The top window always shows a list of the currently active processes, including the names of their owning accounts, whereas the information displayed in the bottom window depends on the mode that Process Explorer is in: if it is in handle mode you'l…
Wireshark - Wireshark is a network protocol analyzer for Unix and Windows. It lets you capture and interactively browse the traffic running on a computer network.
MenuMeters for El Capitan - MenuMeters for OS X El Capitan 10.11 (and later)
SolarWinds NPM - Advanced network monitoring for on-premises, hybrid, and cloud. Download a FREE 30-day trial of SolarWinds Network Performance Monitor (NPM) today!