Anoto licenses a proprietary technology that consists, oddly enough, of... paper.
Paper printed with a special pattern that forms a grid around 60 million Km2 wide, and in which the pen is able to position itself accurately by measuring dot offsets relative to a grid:
The Anoto-based pens then scan the dot patterns upon motion and build a 2D representation of the nib trajectory with a fairly high degree of accuracy.
The major stumbling block for wide adoption, however, is the fact that the pen is useless without special paper with the Anoto pattern. In fact, the whole licensing model revolves around the allocation of specific areas on the complete pattern space to companies like 3M, Esselte, etc., who then print and sell the special paper (at over three times the cost of regular paper).
Oh well. Nothing's perfect, right?
- Pen Roundup
- Overview at myPen - includes a full overview of the technology, features and available commercial services
- Review of the Logitech Io Pen - includes some interesting tests
- handwritten.net - an Open-Source project aimed at developing a sort of "handwriting blogs" and displaying them using a very neat Flash-based frontend to a database application (the project is apparently hosted at SourceForge, but I haven't been able to look at the code yet).