fable is a port of cucumber to php. It can use SimpleTest's browser component to do functional testing.
It's currently quite sparse on features - mostly a proof of concept. It works fine though.
Clone this git repo and make sure that it is included in your path, or that you have symlinked fable to some place that is.
If you want to write functional tests, you also need to have simpletest installed.
fable is an easy and story-driven approach to write high level automated tests (functional tests). It has a guide built in, that will offer you advise as you go along. Try it out now by running fable from the root of your project.