Siege

Siege is an open source HTTP load testing and benchmarking utility. It stresses a single URL with a configurable number of simulated users, or many URLs read into memory, and reports hits, bytes transferred, response time, concurrency and return status. It supports HTTP/1.0 and 1.1, GET and POST, cookies, transaction logging and basic authentication.

Siege is distributed under the GPL v3 and maintained on GitHub; the joedog.org site currently returns an error.