For those of you wanting to run a farm together, you now can! Stardew Valley now has an opt-in multiplayer beta on Steam.
Even better, is that it's cross-platform so everyone across Linux, Mac and Windows can play together! It works with current saves too, but it's best to back them up since it's a beta. Find your saves here "~/.config/StardewValley/Saves".
How to get it?
Right click on Stardew Valley in your Steam library, go to Properties and select the Beta tab. In the password box, enter "jumpingjunimos" and it will then allow you to select the beta from the dropdown menu.
It actually includes a bunch of new content too, however they're not going to tell us what until a later date, you need to find out for yourself! For those wondering, yes—you can marry other players.
Seems like the GOG multiplayer may require Galaxy though and since we don't have Galaxy on Linux, it might be best to pick it up elsewhere for now. There's also LAN support, but online multiplayer is Steam/GOG Galaxy.
See the full details here.