I am interested in what developers are using .NET for. That is C#, MC++, J# and yes, even VB.NET. Really the requirement is the use of the .NET Framework (any version) and that the use is public. Internal projects are great but they are hard to use for advocating the spread of .NET as details are scarce and people invariably cannot use the app.
An app is any publicly available system that uses the .NET Framework in some major capacity. This covers WinForms, WebForms, WebServices and WindowsServices. And if you are using Mono then bring it on.
I am not sure if libraries of code compiled to DLL format is worth listing here. I'd also like to keep the list free of Hello World class apps. We need apps with real meat behind them. The more users the better too. And unless a BETA is really quite advanced and in widespread use it is probably best to wait until v1.0 before listing it.
The more info on the use of .NET in the app the better.