The Steam release of the game is due to release on this date. Naturally, MacGuffin's Curse supports SteamPlay, so a single purchase means you get both the PC and Mac versions at no extra charge. MacGuffin's Curse also features Controller Support (for both PC and Mac) and uses Cloud storage for saves so that you won't lose your progress.
April 19th is also the tentative release date for the Mac App Store and iOS releases of the game - however, unlike the Steam release, these dates are subject to change.