What does this do for you? Well, it provides a pretty GUI interface to your test results. :) It also provides an RSS feed that is updated with the pass percentage of your tests every time you run them. In that way, it's a good fit for continuous integration systems. Finally, once your test plans and test cases have been created by running your tests (via Rake, as usual, for Rails developers), you can add descriptions to the test plans and test cases to help document what you are testing and why.
Now you can brag to your friends about how many tests you have in your app, or show your clients and customers that you actually have tests. :)
I'd like to support other testing frameworks, like jUnit, etc. To that end, the reporting interface is simple HTTP, so any testing framework that allows for a custom reporter and can send HTTP POST requests can send test result reports to Tesly Jr. I'll put up some info about how to construct that request at the site eventually, but until then you can contact me for info about how to do it. I'll be happy to get more frameworks supported by helping you build hooks for your favorite one.