lighttpd - A secure, fast, compliant, and very flexible web-server that has been optimized for high-performance environments
Loader.io - Loader.io is a simple cloud-based load testing service
nginx - A high performance free open source web server powering busiest sites on the Internet.
WebLOAD - WebLOAD - The most flexible and cost effective software for enterprise load, stress and performance testing, integrated with DevOps processes. Click for details
Apache HTTP Server - Apache httpd has been the most popular web server on the Internet since April 1996
StresStimulus - Load testing tool for websites and mobile that works with hard-to-test applications.