Web Testing tools are used to find/identify bugs or errors in a website before it was launched officially for the public on the web. You can find many such tools on the web now a days some are also free.  Here is the list of the finest web testing tools available in the Open source market right now. These tools will not only help you identify the bugs/errors in your website before you launch it publicly but also save your time of finding the suitable Open source web testing tool. 

The grinder is a Java load testing framework that makes it easy for you to run  disorganized testing with the help of many load injecting machines.

This is an open source framework for performance and load-testing. Multi-Mechanize runs concurrent Python scripts to generate load (synthetic transactions) against a remote site or service. This Open-Source tool will help you to create programmatically test scripts to simulate virtual user activity. Afterwards it will generate HTTP requests to intelligently navigate a web site. 

If you want to simplify process of integration testing Capybara is the best solution for you. This open source tools helps to simulate how a actual user would get across with a web application. It is agnostic about the driver running your tests and comes with Rack::Test and Selenium support built in. WebKit is supported through an external gem.

JMeter is an open source software which is specifically designed for testing functional behavior and measure performance. It is used to test performance on both static and dynamic resources such as ( PHP, Java, Files, Perl scripts, Data Bases and Queries, FTP Servers and others). It can be used to simulate a heavy load on a server, group of servers, network or object to test its strength or to analyze overall performance under different load types.  

Selenium is a suite which includes Selenium WebDrivers, Selenium IDE, Selenium Grid, Selenium Remote control which helps to test the web application. Selenium supports some of the largest web browsers like FireFox, IE,Safari,Opera,Chrome which allows you to record, edit, and debug tests. It is also the core technology in countless other browser automation tools, APIs and frameworks. 

 This is a free open source tool for testing performance and scalability of web services. It runs HTTP load tests, which are useful for capacity planning, benchmarking, analysis, and system tuning. This tool is designed for the developers, performance engineers and testers. For the full utilization of this open source tool the developer or the performance tester should have  a good idea about HTTP, XML, and performance testing. Some features of Pylton are HTTP and HTTPS (SSL) support, execution or monitoring console, automatic cookie handling, response verification with regular expressions, cross-platform, real-time stats and more. 

Webrat is another open source tool which enables the developer to quickly write expressive and robust acceptance tests for a Ruby web application. It also supports frameworks like Merb, Rails and Sinatra. Webrat also supports the most popular test frameworks such as: Cucumber, RSpec, Test::Unit and Shoulda. 

Open System Testing Architecture (OpenSTA) is an open source tool which helps to perform scripted HTTP and HTTPS heavy load tests with performance measurements from Win32 platforms. The OpenSTA tools are designed for performance testing consultants or other technically proficient individuals. Results and statistics are collected during test runs by a variety of automatic and user controlled mechanisms. These can include scripted timers, SNMP data, Windows Performance Monitor stats and HTTP results & timings. The tools is free of cost because it is licensed under GPL (General Public License). 

The WebLOAD Open Source Load Generation Engine is an open source project sponsored by RadView Software. This project is intended for ISVs, SIs and software developers who need to integrate a professional load generation engine into their applications.