Dingus is a mocking/stubbing library I've been working on for about a year. It grew out of a now-defunct project's test suite, and I've used it in about 3,500 lines of unit test code. It does two things that are pretty novel:
dyou can say
99 * (d.foo.bar.baz() ** 'hello')and you'll just get another dingus out. This lets you use dinguses to replace dependencies in legacy code without thinking about what interface they must conform to.
The second point above is probably a bit hard to think about from such a short description, so I've created a screencast to show it off. I TDD up a bit of code in the screencast, but it is not intended to be a good example of TDD or test design. I use a lot of stubbing and interaction assertions because I'm trying to show off Dingus' features. In real-world code, you should avoid assertions about object interaction as much as you can.
If you'd like to watch the screencast, it's available on Vimeo, but the version on the page is low quality. If you log in to Vimeo, there's a download link in the bottom right of the page to see it at full quality.