Canoo WebTest
Canoo WebTest is a free Open Source tool for automated testing of web applications. Its power resides in how easily can you set up a functional test, using XML or Groovy, which allows you to add a new layer of validation to your web application.
Canoo has a good integration with Groovy and Grails, but it can be used for applications built on any language, from Java to .Net, including scripting languages like Ruby on Rails, and it has a really good integration with Hudson which makes running the tests even easier.
All in all, if your framework of choice doesn't have a similar tool (or the one it provides is lacking) you should check Canoo. It will improve both your development process and your application.
