http://www.youtube.com/watch?v=z4Y7R54giqM is a video of this system in action.
"The TACO Shell, or TACOS in short, is a replacement Windows® Desktop Shell aimed at supporting shoulder-to-shoulder collaboration around tabletop displays. TACOS is able to rotate each window separately so as to facilitate interaction and visualization for all users present around the table. TACOS also offers a number of additional features to support the management of windows on the desktop: transparency of windows, reduction of windows to their title bar, quick window orientation shortcuts, etc.
... the whole system is built with Tcl/Tk. I (EF) use TkZinc as a replacement for the regular canvas, which gives me the ability to rotate objects and control their transparency. I also use a custom capture DLL for getting the content of the windows. All the rest is a lot of Tcl-glue, some of it being available from my home page [L1 ]"