Something quickly whipped up over a weekend. Nothing fancy, just a little tool to concurrently keep track of the balance per player and transactions between them, on each player's handheld device with a HTML-client, for the duration of a game's session. (You can probably guess which.)
Created with xxm. Based on the EventSource object and a text/event-stream connection, which uses xxm's IXxmContextSuspend.Suspend call intensively to free up worker threads on the server.
Enjoy.