According to Valve product designer Alden Kroll on Twitter, the way Remote Play Together works is that Steam streams the host player’s screen to other participating players while capturing controller or keyboard and mouse inputs from other players, before sending that info back to the host machine. This way, even games that were originally designed as local multiplayer or couch co-op titles can function online without any additional software or patches (though you will need to account for added latency due to streaming).

That means thanks to Steam’s Remote Play Together feature, fantastic local-only games like TowerFall Ascension, Samurai Gunn, or the original Nidhogg could get a new lease on life, as you’ll no longer be required to have everyone in the same room or use third-party apps like Parsec to get the full multiplayer experience.

However, Kroll also mentioned that Remote Play Together was designed primarily for shared-screen or split-screen games like the ones mentioned above, so depending on the specific title, some games may be better suited to Steam’s new online multiplayer feature than others.

[Update: 10/21/19] Today, Valve announced that Steam’s Remote Play Together feature is now available as part of the Steam Beta client. Remote Play Together can be selected from the Friends list via a new option, and includes the ability to play local multiplayer games online with both mouse and keyboard or controller support on PC, Mac, and Linux.