Steam have introduced Remote Play Together

Valve have recently introduced a new innovative feature to their distribution platform, which will allow users to play games that only have couch co-op (aka offline co-op on the same machine) online via internet. Titled Remote Play Together, the new addition to Steam is currently in beta and allows games that were designed for couch co-op to be also enjoyed online at no extra cost and without an overly complicated setup process.

Now in Beta! With Remote Play Together, you can now invite Steam Friends to join your local co-op, local multiplayer, and shared/split screen games online. Up to four players (or even more in ideal conditions), can instantly join in the fun. Only the host needs to own and install the game, while additional players connect through Steam Remote Play streaming technology.

Clients that are interested in testing this new feature will have to join the Steam Beta and after that they'll be able to invite friends from their list to join their Remote Play Together session.

Remote Play Together features:

• Play local multiplayer games with Steam Friends online
   
• Stream video, audio, input, and voice between players
   
• Use your own controllers, or share control of the keyboard & mouse
   
• Play together across PC, Mac, and Linux

You can read more here.