This is a simple Ruby-based policy server to serve Flash's crossdomain.xml policy file. The web is increasingly realtime, but websockets still aren't supported on older browser clients. Many server push libraries (e.g. socket.io) attempt to use websockets, with a Flash fallback. Others (amqp.js, for instance) are Flash only. When using Flash sockets, it's necessary to have a policy server running on port 843, in order to set cross domain policy. This library does the job.