Everyone running Windows Mobile 6.1 or higher is familiar with having .NET CF 2.0 built into ROM. And adding the much-improved .NET CF 3.5 for third-party software  is common.

Evidently Microsoft has updated to .NET CF 3.7, and the .cab file (extracted no doubt from one of the hundreds of "leaked" HTC ROMs out there) is available to install to your device or cook into ROMs.

Changes and improvements are unknown at this time. But if you're feeling adventurous, head over to PPCGeeks or XDA to find out more, including how to get the .cab!