I've used to use and like RSpec. The problem was that it always broke with new versions of Rails and internals were too complex to understand. Then appeared Shoulda and removed the pain of writing RUnit tests, so I switched to using it. But I always missed the elegance of RSpec's matchers.
Until Matchy appeared.
The cool thing about it is that you can create custom matchers easily with #custom_matcher() method provided. Nice.