I was just going to mention the physics engine aspect of it. I saw this in miniature a couple of years ago, when I was experimenting with real-time gaming usin

I was just going to mention the physics engine aspect of it. I saw this in miniature a couple of years ago, when I was experimenting with real-time gaming using web technologies (I know, I know, TCP), but one blocker for low-hanging-fruit projects is that to get a good experience you need client-side prediction, but then it's very hard to get anything like that and also use a pre-existing physics engine. The real problem is: I'm a wuss. Client-side prediction seems like magic to me, and has hurt my head every time I've programmed it, and it goes right back to seeming like magic when I've written it, and I never feel entirely certain that I'm on solid ground. I always come away with the impression that networked physics is hardcore, and I don't have enough chest hair to deal with it. :)