I've spent a few hours with Stardew Valley's online co-op mode and, just like that, I'm one-hundred percent back into the farmer life. I can't stress how weird and wonderful it is to see another player running around Pelican Town after you've spent dozens upon dozens of hours playing alone. It's an altogether different vibe, and your daily chores sure go by a lot quicker with extra helping hands.
Stardew Valley is currently holding a co-op beta on Steam. Here's how you can play:
To enable the beta in Steam, right click the game in your library and select properties. On the window that pops up there will be a 'betas' tab. In the text box, type the password for the branch:jumpingjunimos. Then click the 'Check Code' button.
If you've done that correctly, you will now be able to select the 'beta' option from the drop down box. Once you've done that, Steam will start downloading the update.
In co-op, up to four people can team up, each of which will get their own cabin adjacent to the host player's home. The farm itself, money, and world events are shared, but everyone will have their own skills, relationships, and inventories. So if someone clears a bunch of floors in the mines or builds a bridge, you'll all benefit, but you have to upgrade your tools individually. Time no longer pauses inside of menus, and you also can't go to sleep and turn over to the next day until everyone's in bed.
This developer blog post covers the nitty gritty, with instructions on how to back up your save files (this is still a beta, after all) and how to report bugs. A few other important notes: you can scale the profit margin on sellable items so that you don't get rich too quick, players can marry each other, and there's a text-based chat system complete with hundreds of adorable pixel-art emoticons.
The beta build also has some new single-player features, including hats for your horse, a Winter Market Festival, and new character events and cutscenes. I haven't seen this stuff yet (Ray and I started a new save file for co-op and only just got our first chickens), but I'm sure word will get out soon enough.
Stardew Valley v1.3 Beta [Stardew Valley]