Tabletop Simulator is an engine to enable people to play card and board games online with friends. The fact that only one person in the group has to own the DLC, and that there's a massive Steam workshop of content just makes this brilliant for playing online with friends. It started out a little rough, but recent experiences have been really smooth, with no lag or disconnects. The UI and controls can be a little clunky, but its hugely flexible.
