ObjectiveC2 framework implements the new Apple runtime APIs, introduced with
OS X 10.5 on top of the GCC Objective-C runtime.  Its use is now discouraged.
This code has been merged into the GNUstep Objective-C-2.0 runtime, which can
act as a drop-in replacement for GCC libobjc.  You can find the code here:

svn://svn.gna.org/svn/gnustep/libs/libobjc2/trunk