So it looks like it's a game that's available on GOG, Desura -and- Steam.
List of possibilities:
To The Moon
Blackwell games (only Deception is on Desura)
Anomaly: Warzone Earth
Avernum games (only 4-6 are on Steam/desura)
If that's the case, I'm hoping for Puddle, since it's the only one on the list that I don't have. Then again, though, they might just mean that you get the game on whatever other platforms in addition to GOG, as opposed to it IS on all 3 platforms.