I'd encourage you to play around with Obj-C a little more before writing it off. It's actually a pretty simple, compact and concise language once you dig into it. Apple's APIs, on the other hand... :facepalm:
I’d give it a try if it worked on Windows or Linux. I’m not willing to buy a Mac just to be able to study a language-I could build a Hackintosh but it’s too much trouble for what it’s worth. Most of the languages out there work on any platform. Even C# works on Unices through Mono. But for Apple’s products its always the same story, our way or the highway.
You are correct. GNUstep would be the most well known project to make use of ObjC outside of the Apple world. Also, since it implements the OpenStep API, you could use it to get a basic feel for Mac development without jumping in to the Apple fog.
Which APIs do you dislike? I think Apple's Cocoa and Cocoa touch frameworks are some of the best. Cocoa is old and less polished, but Cocoa touch is pretty awesome.
My only complaint would be how hacked on Core Animation is in comparison with UIKit. For example, WebView doesn't like having a layer, but this isn't mentioned anywhere in the documentation: