HttpWatch : An HTTP Viewer and HTTP Sniffer for IE and Firefox
Wireshark : Wireshark is the world's foremost network protocol analyzer. It lets you see what's happening on your network at a microscopic level. It is the de fac...
Mockbin : Mockbin allows you to generate custom endpoints to test, mock, and track HTTP requests & responses between libraries, sockets and APIs.
Buildbot : Buildbot is an open-source framework for automating software build, test, and release processes.
Mock Service Worker : Mock by intercepting requests on the network level. Seamlessly reuse the same mock definition for testing, development, and debugging.