[makecheck]

I am most curious about GNUstep (gnustep.org). GNUstep is similar to the Window Maker window manager on Linux, like Cocoa uses Aqua on Mac OS X. From what I've seen, GNUstep and Cocoa are very similar (both Objective-C, both using the original NS* classes, etc.) and the project aims to remain compatible with Cocoa where possible. I've used both Window Maker and Aqua, and I like both GUI styles.

Apparently GNUstep is usable on Windows, but I've never tried it.

At least in theory, the same Cocoa-like source could be used for a GUI app on all 3 major platforms.

Objective-C isn't as simple as C, but it's pretty simple, and fully compatible with C. It's also been bound to every major scripting language I can think of.

[andrewf]

There's also The Cocotron, a Cocoa implementation for Win32 - http://www.cocotron.org/Info