I published jSocket on Google Code under the open source MIT License. Remember this is still a work in progress, but it's very stable at this stage. It requires jQuery and Flash Player to run.
On the security front, Flash security does apply. This means however that, with the proper security policy server side, you are able to make cross domain connections.
The only drawback is that Flash expects zero terminated packets and because the sockets were intented for XML data, you can only send wrapped binary data, for instance wrapped in base64 strings. Flash also sends out zero terminated packets.
So check out jSocket on jsocket.googlecode.com where you can find information, documentation and examples.