I've found https://blockchain.info/api/api_websocket really handy for watching addresses and transactions in realtime web apps with javascript.  I tried to ask blockchain.info if the implementation of this API is open source somewhere and didn't get a response.  I don't see it on their github page.  Does anyone know how this is implemented or if there are any open source alternatives that I could host myself?  Any ideas what technologies might be used to create an API like this?  socket.io? bitcoind or bitcoinj?