Jay B. Harlow [MVP - Outlook] wrote:

These are coming along nicely - though there is no proper Forms
implementation yet (although they're working on using Wine to provide a
full port - although .NET claims to be platform-agnostic, the Forms
portion is VERY closely tied to Windows). There is, however, a
GTK-based GUI framework for Gnome (GTK#). So GUI-wise you'd likely have
to fork code.

There's the DotGNU project too (www.dotgnu.org).
They have OSX support as well (not sure about Mono in that respect) - so
your app would run on a Mac too.