Charles Proxy - HTTP proxy / HTTP monitor / Reverse Proxy
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.
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.
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.
Postman - The Collaboration Platform for API Development
Zabbix - Track, record, alert and visualize performance and availability of IT resources