Initially released as a single-player game, Stardew Valley is a farming RPG that had planned to have a multiplayer component sometime post-release. The game exploded in popularity, and eventually, Chucklefish came on board to provide additional support for publishing & development. Those resources have been put to good use for fleshing out the multiplayer portion of the game. Tom Coxon of Chucklefish is the man who's done the brunt of the work on the network code necessary to get the game working in a multiplayer environment, something that ConcernedApe considers an "impressive feat."
Work on the new features for the 1.3 patch has been completed. The newly-introduced text has been sent off to its respective places to be translated while the developers work on bug fixes. As soon as the translated text is integrated into the game, an internal QA phase will begin to test all of the new features in single-player and multiplayer environments. Once that's done, Stardew Valley should be ready for a multiplayer beta to go out to players. ConcernedApe anticipates a Spring 2018 release date. We'll get a concrete date as they get closer to wrapping up all of the necessary testing.
As a bit of a consolation prize, the screenshot in the header was released to show off the new signs feature. Signs will be available from the outset of the game. Any item in the game can be placed on the signs.
The multiplayer beta was supposed to release at the end of 2017, but it ended up getting delayed until sometime this year. We've had some insights into what the next patch will include in development updates, including how the hosting scheme will work and what sort of other content we'll be getting, regardless of whether or not you'll be playing with a friend. You can grab Stardew Valley for the PC via Steam, Xbox One, PlayStation 4, Nintendo Switch, and who knows what else in the coming years.