Tue Aug 10, 2010 10:57 pm by watusimoto
It's basically a data format, and when you download the file at the link posted by Bobdaduck, you will get an up-to-the-second (well maybe 30 seconds) status report of what is going on at the Bitfighter master server.
There are many bits of code out there for parsing JSON, and if you are writing in Javascript, parsing is trivial even without a library.
So it should in principle be very easy for someone (i.e. not me) to write a widget that checks the master server every 20 seconds and displays an alert when someone joins a game, or some other criteria is satisfied.