UPDATE: Mac users should now be able to play StarMade correctly. If you have any issues launching the game still, please open a support ticket at http://help.star-made.org/.
Greetings,
Currently Mac compatibility is broken (for Steam StarMade), we're currently working on this issue. We hope to have this fixed and ready for you by the end of the day. If you are a mac user, it would probably be best to wait until we have fixed this issue before purchasing.
In the mean time, Mac users can still play and create an account to the full free alpha access version offered on our own website. Download here: http://star-made.org/download
You will be able to play the current version of the game with this, test it out and have fun.
Sorry for this issue and delay.
- SM Team