Apache JMeter
Apache JMeter is a 100% pure Java desktop application designed to load test functional behavior and measure performance. It was originally designed for testing Web Applications but has since expanded to other test functions.

Canoo WebTest
Canoo WebTest is a free open source tool for automated testing of web applications. It calls web pages and verifies results, giving comprehensive reports on success and failure. The White Paper provides an overview of the features and the design rationale. Detailed information is provided in the Syntax Reference and the Install and Troubleshooting guides.

HtmlUnit
HtmlUnit is a java unit testing framework for testing web based applications. It is similar in concept to httpunit but is very different in implementation. Which one is better for you depends on how you like to write your tests. HttpUnit models the http protocol so you deal with request and response objects. HtmlUnit on the other hand, models the returned document so that you deal with pages and forms and tables.

HttpUnit
Written in Java, HttpUnit emulates the relevant portions of browser behavior, including form submission, JavaScript, basic http authentication, cookies and automatic page redirection, and allows Java test code to examine returned pages either as text, an XML DOM, or containers of forms, tables, and links.

jWebUnit
jWebUnit is a Java framework that facilitates creation of acceptance tests for web applications. It evolved from a project where we were using HttpUnit and JUnit to create acceptance tests. As the tests were being written, they were continuously refactored to remove duplication and other bad smells in the test code. jWebUnit is the result of these refactorings.

Latka
Latka is a functional (end-to-end) testing tool. It is implemented in Java, and uses an XML syntax to define a series of HTTP (or HTTPS) requests and a set of validations used to verify that the request was processed correctly.

MaxQ
MaxQ records you using a web site. It turns the links you click on and any other input into a Python script that you can play back at any time. You might use it to: Check that your web site still works (regression test); Check that your web site is producing valid HTML (using JTidy); Automatically extract information from, or take some action on, someones else's web site.

SlimDog
SlimDog offers a simple script based webapplication testing tool. It is based on httpunit. The tool offers a wide range of commands to work with forms, check the content of tables and navigation between HTML pages. Rather than writing long JUnit testcases or crucial XML files the users can write simple text scripts.