I've used the rare book readers at the British Library, and liked them quite a lot. While they didn't include every feature one could imagine, they did have a very intuitive interface. (The readers actually in the British Library are better than the online version, because their screens are desk-sized.) UM has a rare book reader too:

Modeled on similar projects at The British Library and the National Library of Medicine, our “PictureIt” site puts some of the most beautiful and sought‐after items in our collections into the hands of readers worldwide – virtually.

The Visual Understanding Environment (VUE) is an Open Source project based at Tufts University. The VUE project is focused on creating flexible tools for managing and integrating digital resources in support of teaching, learning and research. VUE provides a flexible visual environment for structuring, presenting, and sharing digital information.

heads up, fellas, cool apps everywhere. We gotta get on the ball ;-)

Take a look at the visualization of languages, and then look at http://flare.prefuse.org/demo >> Layouts >> Sunburst

I can think of some cool language apps (iPhone for ex.) we could build like this