Your Steam build should update right away with Mac and Linux compatibility!
Steam cloud saves are integrated and will allow you to access your save files across all platforms.
Multiplayer, version 1.1, console ports and localization are all still in the works and I'll update everyone as soon as more info is available.
If this will be your first time playing Stardew Valley, thank you and I hope you have fun!
Also... thanks so much to everyone who helped test these builds before launch <3
-ConcernedApe