The PushToTest TestMaker suite is a powerful tool for the testing of web services and applications. Paired with a highly flexible and comprehensive Jython implementation, TestMaker gives the developer all the tools they need to thoroughly test an application. Web applications are becoming increasingly sophisticated, and flexibility is needed to truly provide an accurate testing environment.
The Grinder is an open source load testing solution that operates on a Java Virtual Machine. This gives The Grinder a great degree of portability. The tool is also exceedingly simple to set up, requiring only that the user follow a few simple steps. Installing The Grinder is as simple as downloading a JAR file and placing it in the correct CLASSPATH. Once this has been done, the program is easily invoked from the command line.
As an open source solution to the load testing demands of complicated Web 2.0 applications, Tsung offers engineers a cost effective and thorough means of testing. 
Written in the concurrency language of Erlang, Tsung is dedicated to providing an intense load while running a software stress test. Capable as well of running in a distributed mode, Tsung can simulate thousands of users accessing resources at the same time.
When designing a web architecture, it is crucial that the server be capable of handling heavy loads. While this is an important requirement of any web design project, it is also difficult to perform realistic testing with human users. The sheer number of users and machines needed to provide a realistic test make such manual methods prohibitive. This is where utilities such as JMeter step in, making such “load testing” possible without legions of volunteers.
RSpec is a tool produced with the intent of making use case testing simpler in Ruby. Traditional Ruby on Rails unit testing can become complicated and hard to manage when working with a large project. The harder the testing becomes, the more time that unit testing consumes. With RSpec, however, testing scenarios are put in simpler terms and the Ruby code to do the test is generated automatically. This can do wonders to simplify unit testing.
WebLOAD is a tool for functional and load testing your web services. It provides recording functionality to automate test creation. Some components of this application are open source. However, The Console and IDE source portions of the overall program are still proprietary, but are available for free in binary format. The project appears to be active, both internally and externally. Please refer to the WebLOAD home for a full description.
Selenium is an open source project dedicated to providing a simple and flexible means of web application testing. Unlike client side load testers such as JMeter, Selenium is intended to test for correctness of presentation and functionality. As a testing tool, Selenium offers a finer level of control over the actions of virtual users. Developed as a Firefox plugin, Selenium users can quickly build complicated tests that involve navigating through several pages. This allows an engineer to create tests that mimic typical user behaviors, such as logging in and interacting with the web site.
Websites have evolved significantly since the inception of the internet from simple pages that conveyed information to interactive entities that users can manipulate and utilize for many different purposes. As websites evolved and became more complicated so did the possible interaction between web users and websites giving websites more and more complicated programs, applications, and coding. The increased functionality of websites made them more useful for visitors but also created more ways for the new more complicated programming to fail.
Selenium Core is a software testing tool for website applications. With this test program web developers can test the functionality of their website applications with a variety of browsers and under a variety of conditions simulating the different visitors that can use the web site. Selenium Core runs directly in a browser just like real users and supports different operating systems, Windows, Linux, Mac, and browsers including Internet Explorer, Mozilla and Firefox.
This open source Apache project is available at http://jakarta.apache.org/jmeter/. JMeter is a mature project with many contributers that was originally developed by Stefano Mazzocchi of Apache. It is a Java desktop application that is used to simulate a load on a web server, web application or other network resource. JMeter is an active project with 200-500 postings a month on its user mailing list and hundreds more on its developer mailing list.