mitmproxy : mitmproxy is your swiss-army knife for debugging, testing, privacy measurements, and penetration testing. It can be used to intercept, inspect, modify...
Zombie.js : Zombie.js is a lightweight framework for testing client-side JavaScript code in a simulated environment. No browser required.
GoReplay : GoReplay is an open-source tool for capturing and replaying live HTTP traffic into a test environment in order to continuously test your system with r...
vegeta : Vegeta is a versatile HTTP load testing tool built out of a need to drill HTTP services with a constant request rate. It can be used both as a command...
Mockbin : Mockbin allows you to generate custom endpoints to test, mock, and track HTTP requests & responses between libraries, sockets and APIs.
toxy is a fully programmatic and hackable HTTP proxy to simulate server failure scenarios and unexpected network conditions, built for node.js/io.js.