Interactive whiteboard design

I am starting to learn that there are many design choices when it comes to classroom interactive whiteboards.

From a hardware standpoint I see 4 main choices on the market right now:

1) A touch-sensitive whiteboard that connects to your computer and digital projector.   In the past when I heard someone say smart-board this is what came to my mind.

2) Interactive projector that connects to your PC and then used with your computer and classroom whiteboard.

3) An interactive device that attaches to a classroom whiteboard, connects to your PC by wire or wirelessly and then used with your computer and projector.

4) This seems to be a new entry.  It is a combination short throw projector and interactive-whiteboard.

If you know of any other designs let me know.

Each of the above designs is limited by the manufacture’s software features which will be a great subject for another post.