There are some things that modern browsers do that most people do not realise, and which are awesome. One is svg, which is a whole other blog post, but the other is websockets.
They are awesome as they allow a web page to connect to some resource and keep that connection alive and open whilst that page is open, and asynchronously send or receive data on that connection.
Yes, this seems like something that has been possible on an RS232 cable for a while, but actually from a user interface point of view it is pretty big. It allows messages (blocks of data) to be sent and received. I am using JSON objects, but it could be anything.
My main application, and why I put together my own websocket server library, is to allow my alarm system to do stuff using web sockets. It means we should be able to do a floor plan with images of PIRs and doors and all sorts, updating in real time, and clickable to do things. That will be magic for installing the alarm and walking around with an iPad, but also for remote monitoring. Imagine making a page with embedded security camera footage, and so on in with sensors and doors and so on.