I have for a while tried to look into how to create interactive patterns. I do most of my grading in spreadsheets and thought why not make the functionality available to knitters of my designs?
My ultimate idea was to allow knitters to input for instance gauge and body measurements and - voila, a personalized sweater pattern would pop up! So I have tried out several online spreadsheet solutions, but the few that actually could be embedded in a web page had a terrible layout and not really user friendly. In the end, the optimal solution seemed to be based on Java scripting, but I have been a bit reluctant to pursue that direction, because it would require a complete restructuring of my web pages. If I had all the time in the world, maybe...
However, then I found out - via a Ravelry forum, naturally - that Scribus supports Java scripting, which means I can create interactive pdf files! Scribus is an Open Source Desktop Publishing program, very easy to use, even for someone like me, who usually is most comfortable using LaTex for word processing, because all layout issues are taken care of beforehand. After having tried Scribus, I even consider to rework all my patterns, also the ones that don't require interactivity.
I am almost done with a generic sock pattern and have finished a prototype of a pattern that estimates how many stitches to pick up along a bias edge. I am having so much fun! Here is a preview of the bias edge estimator: