May cool applications out there are using Microsoft's .NET Compact Framework today but so far, the CF for Windows Mobile devices had a serious issue: you had to install it on your device, it wasn't possible to install CF on memory cards. Unfortunately, the .NET Compact Framework is pretty big which means - in worth case - after you've installed the .NET CF on your device, you hadn't had enough space to install the application but now comes the good news: Microsoft recently released the .NET Compact Framework 2.0 Service Pack 1 which can be installed on memory cards now as well.
The Microsoft .NET Compact Framework 2.0 SP1 Redistributable contains the common language runtime and class libraries built for the .NET Compact Framework. In addition to supporting version 2.0, it also supports applications developed for version 1.0 and service pack releases before version 2.0.
This redistributable enables running .NET Compact Framework applications on the Pocket PC, Pocket PC Phone Edition, Smartphone, and other Windows CE powered devices and uses ActiveSync 4 and up to update the device.
Microsoft .NET Compact Framework 2.0 SP1 works with Windows Mobile 2003 for Pocket PCs; Windows Mobile 2003 for Smartphone; Windows Mobile 2003 SE for Pocket PC; Windows Mobile 2003 SE for Smartphone; Windows Mobile 5.0 for Pocket PC and Windows Mobile 5.0 for Smartphone. It's available for free from Microsoft.
Cheers ~ Arne