Just like NCrunch, it executes your code while you type. But instead of test outcomes, it focusses on the details of the code execution and provides invaluable insight into the contents of variables and even the control flow as you type. You can even drag a slider to see different iterations in loops. All you need is a starting point like a static method, a test method or any method where the parent type can be instantiated with some generic defaults.

This short video (~6 minutes) gives a great first impression so far:

I might take a look at the free 30 day trial as soon as I am back in Visual Studio.