I’ve always quite liked air hockey, in spite of being quite bad at it. One of the other teams in the lab I work in has built an air hockey game which works with two players at a distance. Each person gets half a table, a projection screen and so on. While I’m sure there’s a lot more to the research behind it, than just ‘wow, it would be cool to play air hockey over a network’, it really does sound cool. I haven’t actually played with it, but really should con someone into giving me a demo sometime.