We have developed a simple massively multiplayer online game system as a test bed for evaluating the usefulness and performance of JCSP.net. The system consists of a primary login server, secondary servers managing play on geographically distinct playing fields, and an arbitrary number of players. The basic structure of the game system is fairly simple, and has been verified to be free from deadlock and livelock using CSP and FDR. The JCSP.net implementation is straight-forward and includes over-writing buffers so that disconnected players will not block the servers and other players. Performance tests on local area networks under Windows demonstrate that five secondary servers easily support 1,000 machine-generated players making moves every two to five seconds. The player move end-to-end time was about 65 milliseconds, which is considered fast enough to support fast-action online games. Conversion from Windows to Linux required minimal effort; limited tests confirmed that versions using Linux alone, and Windows and Linux together, were also successful.