We've had an idea for a new project for some time, and we've finally decided to put out a code seed for it to see if the community wants to get involved.
The idea is this - Create a native coredll.dll library for the desktop that exactly matches the one exposed by Windows CE (same funtions at the same ordinals). In theory, this would allow you to run Compact Framework applications against the full framework including code that P/Invokes. The long-term goal is to implement every funtion (there are about 1800 of them, we've seeded the project with 50), but the milestone I'm shooting for is to get this library to a point that the SDF will run on the desktop.
Why would you want this library you ask? The answer is fairly simple - to help in debugging and unit testing. I don't envision you shipping a product that runs on CE and XP, but I do see great value in being able to run your CF assemblies through NUnit or Team Suite unit tests, which today cannot be done on a device. This project is an enabler for that.
THe project is located at CodePlex as the OpenNETCF Advanced Debugging Toolkit. Look for more pieces to the toolkit as time progresses.