I was playing around with the 7-point story structure popularized by Dan Wells recently, and while a spreadsheet was fine for setting up the various plot lines, I found layering them all together in a spreadsheet to be annoying. Especially since I was trying to handle 7 different plot lines.
So, of course, I created a tool to help handle this. I ended up writing it in HTML+JS+CSS, this makes it so that once you download the app (6 files), it runs entirely in your browser, and no information is transmitted.
You can also play with it online here.