Apart from Fitnesse is there anything like concordion for .NET?
Concordion is an open source framework for Java that lets you turn a plain English description of a requirement into an automated test
David Peterson (the author of Concordion) has told me that there is no .net port of Concordion that he knows of. However he says I should look at Nbehave (and here) as well as FitNesse.
I have also found Twist that Thoughtworks Studios has just released, it is not cheep. It claims to support Selenium and Frankenstein out of the box, on a quick look, its Domain Specific Languages look a lot like Concordion. However it is Java, not .NET Thoughtworks claims..
Twist is the next generation of software test automation tools. It provides a rich environment for authoring, executing, and maintaining tests.