SlowHTTPTest is a highly configurable tool that simulates some Application Layer Denial of Service attacks by prolonging HTTP connections in different ways.

Use it to test your web server for DoS vulnerabilites, or just to figure out how many concurrent connections it can handle. SlowHTTPTest works on majority of Linux platforms, OS X and Cygwin - a Unix-like environment and command-line interface for Microsoft Windows, and comes with a Dockerfile to make things even easier.