We are looking for a screen sharing application similar to Other screen sharing applications, basically all participants can see the screen of the Master, The person presenting can pass control of there computer to another participant who is using the flash client.  The master does not have to use the flash client.  Participants need to enter a code in order to see the presenters screen.  The client side needs to be able to have the presenters screen fit on there screen, so scaling on the client side is required.  The presenter needs to work on Mac,Linux,Windows and it must allow you to select a portion of the screen to share, or share the whole screen.