What is it?
gadgets.realtime and the APIs built on top of it allow gadget developers to write applications that communicate asynchronously with another endpoint, whether that endpoint is another instance of the application (on another machine, or in another browser, for example), the container hosting the gadget, or an application hosted in the cloud.
"With this API, you can share an object between instances of a gadget, and be notified in realtime when the other instance modifies it. More APIs and UI improvements to allow gadgets.realtime gadgets to be used on orkut and iGoogle are in the works and coming soon."
"The idea is that developers can build mini-applications that can allow real-time user interaction through the instant messaging foundation of Google Talk IM. Lettvin showed off an example of a chess game that was not only discussed over IM but played through an interface with IM-like communication infrastructure running underneath it. That's pretty hot."
If you are interested, here's the discussion group