I'm in the process of learning Objective-c but would like to run code snippets via some sort of emulator on Windows — preferably web based.
I want to understand Objective-C syntax and walk through common code examples, probably via some sort of console. I would probably leave any framework type learning for when I get onto my MacBook, at home.
I have done a quick Google with no success.
AFAIK you can use the GNU compiler to compile Objective-C, so that should be usable on Windows too. This should be sufficient to get you started with programming the language.
For Mac OS X however the language is only part of the equation, you will want to program against the libraries of Mac OS X, and for that you will really need a machine running it.
It depends what you mean. Objective-C can be compiled by GCC, so you can happily create Objective-C test apps on Windows. If you are talking about the frameworks though, which contain most of the power when developing on OSX then it's a no unfortunately. You can get libraries compatible with SOME parts from gnustep.org (and run them on Linux/BSD), but it's still not the full OSX "stack".
You can get OS X running in VMWare, but it's illegal, so you best bet is to pickup a cheap Mac that can run Tiger/Leopard and use that.
I'm not sure which libraries are present and which are not but you can run OS X Server in a VM (providing you have an OS X Server license of course). This would allow you to have a virtual Mac environment on your Windows system.
As has been mentioned above, there's no way to achieve what you want natively within Windows as the underlying system is obviously different.
Good luck.
Another possibility is to use Cappuccino.
It is a cocoa-like framework for javascript, and looks very similar to objective-c. The language is called objective-j.