Intermind Communicator product (which really opened my eyes to the possibilities of the Web):
Intermind Communicator relies on the Web for transport and display, but builds in the active part of email, changing the dynamic of the communication process. Let me give an example of how this will work with TidBITS, since TidBITS is also being published via Intermind Communicator, using what Intermind calls a 'hyperconnector,' a small file that contains information about the item being published, including publication name, description, polling frequency, and so on.
First off, you install Intermind Communicator, which runs on your computer and uses a Web browser as its interface. If you want to receive TidBITS via Intermind Communicator, you subscribe to our hyperconnector, which is a matter of following a Web link to download the hyperconnector file and automatically add it to your Intermind Communicator database. Once that's done, Intermind Communicator reads the contents of the TidBITS hyperconnector and checks our Web server for updates once each day.
At its base, it's a database combined with a Web server that only works for a Web browser on the same machine.
The cool thing about Intermind Communicator - which sunk many years ago - is that it was an HTTP server on the desktop. Just like Google Desktop Search is today. And UPnP in Windows. And so on...
(But they don't have the cool 90's icon of Intermind...)