This is Apple's Objective-C Runtime, as available from the Apple's website: http://opensource.apple.com/source/objc4/objc4-437.1/
Apple does unfortunately not provide a direct download link, hence this repository on GitHub.
Copyright (c) 2010 Apple Inc. All rights reserved.
This file contains Original Code and/or Modifications of Original Code as defined in and that are subject to the Apple Public Source License Version 2.0 (the 'License'). You may not use this file except in compliance with the License. Please obtain a copy of the License at http://www.opensource.apple.com/apsl/ and read it before using this file.
The Original Code and all software distributed under the License are distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. Please see the License for the specific language governing rights and limitations under the License.
Owner: Jean-David Gadina - XS-Labs
Web: www.xs-labs.com
Blog: www.noxeos.com
Twitter: @macmade
GitHub: github.com/macmade
LinkedIn: ch.linkedin.com/in/macmade/
StackOverflow: stackoverflow.com/users/182676/macmade