croquet is very fast, and simple. However, if the relay server has no state whatsoever, this means that you can have conflicts between shared resources. Most multiplayer games i am aware of, have a server which is stateful, and enforces various rules, and dishes out exclusive resources, and arbitrates between the clients. Handling latency effects gracefully is an art form, and there are surprisingly few programmers who have built the networking stacks for various games. It is a super-narrow specialty of the programming industry, those people who know the networking aspects very well. Making sure that lower latency doesn't give you too much of an advantage is a very subtle area for which i have the highest admiration. I sure hope they have good debugging tools; it is no easy thing to debug multiple computers running in parallel at a distance, with lag times, and retransmissions causing random fluctuations in arrival time of correct packets.