Mono, more on cross-platform
Mono (very different from mono), is, at its core, an implementation of the Common Language Specification - which we purposefully made public domain through ECMA. Mono is pretty cool, too, and I'm personally glad to see it. They even praise the standard Microsoft helped develop:
The Common Language Infrastructure platform is similar to the goals we had in GNOME of giving language independence to programmers. It is more mature, documented, larger in scope, and has a consistent design.
What makes the Common Language Infrastructure development platform interesting is that it is a good mix of technologies that have been nicely integrated.
Which is a welcome change from what we usually hear from the open-source community. Garrett mentioned:
Without System::Windows::Forms , having the CLR on Mac OS X and FreeBSD is kinda like a mule with spinning wheel : no-one knows how he got it, and be damned if he knows how to use it :)
Well, Lyle... I mean Garrett, remember that the SSCLI is in its first version - not everything is there yet. And GTK# looks like a fairly good idea. But the truth is that Windows::Forms is a COM-interop wrapper for the native Win32 GDI, which hasn't been ported to other platforms, and likely won't be - except by those great people over at WINE :). What you ought to be wondering about is WinFX. And I don't know the answer to that question...