Runscope – API Tools for Developers
runscope.com
runscope.com
I typically like to do more and more things in a terminal rather than in a GUI or web interface, especially for that kind of things, but there's definitely benefits in having all requests logged and easily accessible and editable.
Some aspects look like a very nerdy version of a social network (stream, share, favorite), which is kind of surprising but I could see how that would be useful sometimes. I have a backburner project using the Heroku API (which I've found acting weird sometimes) and that should be a good way to test it more.