The Ruby library, Octokit.rb, has been developed by the Ruby community over several years and now with GitHub’s announcement has been given the ‘official’ status.
Octokit.objc on the other hand is a result of work carried out by GitHub’s Mac development team. Built using GitHub’s Mantle model layer, the library “is a Cocoa and Cocoa Touch framework for interacting with the GitHub API.”
Released under the MIT license, the source code of the two libraries is available on GitHub web site. The announcement on GitHub’s website notes that the release is of “first two libraries” indicating that the code-hosting service may be planning to expand and release Octokit in the future.