Cocotron is an open-source cross-compiler for Objective-C. Its goal is to help compile Obj-C source code and Apple frameworks on Windows 2000 - 7.
The purpose of Cocotron is to provide a cross-platform compiler for objective-c development. It provides source code level compatibility with some of Apple's frameworks.
Cocotron aims to allow developers to compile for any desktop platform. However, most of the project is focused on Microsoft windows (mainly versions 200 thru 7).
Cocotron is a collection of well known and popular open source tools, specifically gcc, binutils and mingw, which are organized and patched to support the Cocotron project.
Cocotron is intended to be used from within Apple Inc.'s xcode as a cross-compiler, and Cocotron itself is an Xcode project.
The Cocotron project page is available here.