A bit like Skype, but instead of sharing the output of a webcam, you'd share a chunk of your screen. The chunk would be resizeable, just like a standard window.
The box would apply not only to visual data, but also audio - the person on the other end would only hear the output of programs within the selected area.
There would also be a file sharing feature which would allow users to simply drag and drop from the shared window to their own desktop.
I'm not sure how, but there would have to be some kind of feedback loop blocker in case the two shared windows overlap.
--EDIT-- Only one user would be allowed to share their desktop at a time for the sake of feedback prevention, but there would be a button on the window that would allow for instantaneous switching and a chat window to facilitate communication.-- Joolin, Oct 29 2009 Is this so you can chat to friends using IM, watch a movie you downloaded in a player, and still share that little bit of your desktop you are doing work in with your boss? (Or is there another reason you want this?)-- vincevincevince, Oct 29 2009 Actually what made me think of it was wanting to collaborate in FLStudio (a music sequencer/synthesizer program) in realtime, but you could use it for just about anything.
Actually the whole realtime collab thing gives me another idea, soon to be posted...-- Joolin, Oct 29 2009 Baked. The current beta of Skype can do the visual part, the audio can be routed fromn anywhere.-- loonquawl, Oct 29 2009 When you say Skype can do the visual part, do you just mean the camera or can it be a monitor output?-- Joolin, Oct 29 2009 random, halfbakery