The mac and linux builds both function and compile. Both of them still need some work in terms of making sure basic stuff works correctly. Most of the specific work is just making it play nice with OS specific features we need to support. The plan is to roll them out as soon as we can during the alpha. Mac is slightly easier and will probably come online first. I don't have an exact ETA right now because it depends on how the next few days of the windows alpha rollout goes. We are still absolutely dedicated to mac and linux and they will both show up during the alpha.