Easy acceptance testing with specification

I look for a tool/framework to make automatic acceptance-testing. The interface to create new tests should be so easy, that a non-programmer (customer, boss) will be able to add specifications for which will be tested automatically. It should be some way to execute the tests from command-line, to include a run of the tests in automatic builds. I prefer Java and Open-Source, but my question isn't restricted in that way. What do you can recommend and please explain why your tool/framework is the best in the world.