From reading the description, and from what little I know about IronPython...<p>IronPython is a re-implementation of Python in C# which allows it to play nice with .NET.  This is similar to Jython which is a re-implementation of Python in Java that plays nice with the JVM.<p>This project on the other had is not a re-implementation at all, but aims to augment the existing CPython implementation with JIT APIs and is using CoreCLR for the JIT.