When Valve's popular Steam distribution system was released for the Mac last week, Muse Games's Alex Jarocha-Ernst wrote the following:
Muse Games just released our game "Guns of Icarus" on Steam! Thanks to Unity's cross-platform support, we were able to be one of the first SteamPlay games available.
Guns of Icarus, as well as Max and the Magic Marker and Bob Came in Pieces are all Unity games which were available at launch as "SteamPlay" games — games which you can buy on Steam and then download for either Mac or PC, or both. I had to find out more, so I contacted Austin Lane, one of the founders of Muse Games.