Deluge is a Web site load tester. Simulates multiple user types and counts. Includes proxy server for recording playback scripts, and log evaluator for generating result statistics.
FunkLoad is a functional and load Web tester whose main use cases are functional testing of Web projects (and thus regression testing as well), performance testing, load testing (such as volume testing or longevity testing), and stress testing. It can also be used to write Web agents to script any Web repetitive task, like checking whether a site is alive.
Hammerhead 2 is a stress testing tool designed to test out your web server and web site. It can initiate multiple connections from IP aliases and simulated numerous (256+) users at any given time. The rate at which Hammerhead 2 attempts to pound your site is fully configurable, there are numerous other options for trying to create problems with a web site (so you can fix them).
Siege is an HTTP regression testing and benchmarking utility. It was designed to let web developers measure the performance of their code under duress, to see how it will stand up to load on the internet.
SIPp is a performance tester for the SIP protocol. It comes with a few basic SipStone user-agents scenarios (UAC & UAS), establishing and releasing multiple calls with the INVITE and BYE methods.
Tsung (formerly known as IDX-Tsunami) is a distributed load testing tool. It is protocol-independent and can currently be used to stress HTTP and Jabber servers. It simulates user behaviour using an XML description file, reports many measurements in real time (statistics can be customized with transactions, and graphics generated using gnuplot). For HTTP, it supports 1.0 and 1.1, has a proxy mode to record sessions, supports GET and POST methods, Cookies, and Basic WWW-authentication. It also has support for SSL.
Web Performance Suite
(commercial) The Web Performance Suite is a suite of testing tools for web servers, including load testing, web page performance analysis, and coming in 2006 functional testing and performance monitoring. The statistical analysis in the Load Testing Module takes your site's performance criteria, and determines the number of users your Web site can handle. Because data is collected at the URL level, it not only identifies slow Web pages, but identifies the particular part of the Web page that caused the problem. It includes hard-to-find features such as IP spoofing, client certificates, multiple simultaneous test cases, authentication, SSL recording and playback, automated analysis, AJAX support, SOAP support, and more.
Web Performance Trainer
(commercial) Web Performance Trainer is a load testing and stress testing tool for Web servers. Its statistical analysis takes your site's performance criteria, and determines the number of users your Web site can handle.
WebLOAD Open Source
WebLOAD is a commercial-grade load and stress testing tool. It can load-test any Internet application, including applications that use Web 2.0 and AJAX.
Webmetrics is focused on providing tools to help with rapid, remote, and automated usability testing and evaluation of web sites.
XCache is a fast, stable php opcode cacher that has been tested and now running on production server under high load. It support and is tested on all lastest php cvs branches, such as PHP_4_3 PHP_4_4 PHP_5_1 PHP_5_2 HEAD(6.x)