If they insist on pushing Mac OS AND want to be seen as a good free software citizen they might want to consider putting some effort in the GNUstep project. Once GNUstep is up to par they should be able to build for that on Linux and Windows with minimal porting efforts.
Still, I'm disappointed in the lack of vision many of these so-called 'open source' companies exhibit. Don't they realise that by pushing these closed, proprietary platforms they undermine the very base of their own existence? The software and community which github depends on was not the result of the generous sponsorship from Microsoft and Apple after all...
Fishy practices, sounds like Apple. It checks out.
Remember what happened when Linus decided he wanted use BitKeeper to maintain Linux? Also remember how that worked out in the end? Free and/or open source software and closed, proprietary companies often make odd bedfellows.
Does nobody at github have any sense of ethics? Github was built on open source software and Linux. Why not give something back? Why support those who spend national budgets on anti open-source lawsuits?