With the launch of Stadia, cloud gaming has received a ton of public attention, and many other companies working on game streaming have benefitted from the curiosity, too. In fact, Steam has had Remote Play, its own local-machine-based streaming service, for a long time already, and now a neat addition to it has left its beta tag behind. It's Remote Play Together, and as the name suggests, it lets you share local multiplayer games online with up to four players.
To start playing with your friends, just head to the Steam menu in any supported game, select a contact, and choose "Remote Play Together." After they accept the invitation, you're able to play together. You can adjust the master volume for all participating parties, and a voice chat connection is automatically established. Everyone is able to use their own controller, but if your friends don't own compatible peripherals, it's also possible to share keyboard and mouse input from the streaming machine. Steam says that up to four players can join in, "or even more with fast connections."
Since the service is accessible on Steam Link and Steam Chat, you can make any supported game cross-platform and play it with friends on Windows, Android, iOS, macOS, and Linux. Steam says it should be possible to play titles with little to no lag when your upload connection is fast enough, but I'd be skeptical about that claim, especially the more friends you add into the mix.