The Concordion.NET framework brings together testing and specification. Concrete examples of expected behavior (written in HTML) can be instrumented with Concordion commands that run tests against the real system via fixture code. Fixtures helps to decouple the specs from the system under test.
These executable specifications you find here are used for the development of Concordion.NET. They show how you can use the features of this framework. Additionally, they can be used as real world examples of Concordion.NET itself.
See here for a simple example.