This is a similar tool as http://httpbin.org/ which was written by Kenneth Reitz to test python request http://python-requests.org/. I like that this is written in tornado thanks for sharing.
One difference is that pathod (and pathoc, the client-side equivalent) works hard to make it possible to violate the HTTP protocol specs at will, in pretty much arbitrary ways. The next version of pathod also moves away from Tornado to let it take more direct control of comms.