mitmproxy : mitmproxy is your swiss-army knife for debugging, testing, privacy measurements, and penetration testing. It can be used to intercept, inspect, modify...
httpbin.org : A simple HTTP Request & Response Service.
Siege : Siege is an http load testing and benchmarking utility. It was designed to let web developers measure their code under duress, to see how it will stan...
Vcr : Record your test suite's HTTP interactions and replay them during future test runs for fast, deterministic, accurate tests.
Hurl : Hurl is a command line tool that runs HTTP requests defined in a simple plain text format.
It can chain requests, capture values and evaluate queries ...
toxy is a fully programmatic and hackable HTTP proxy to simulate server failure scenarios and unexpected network conditions, built for node.js/io.js.