Twine is a fantastic, FREE, open source story telling tool that allows the writer to create non-linear stories in an HTML format. Think of it as a program to write your own choose your own adventure. For information and samples of Twines created by other users check out this post board
For a total beginners guide to starting with Twine check out this guys site
For a quick and dirty cheat sheet on getting started with Twine, check out this great resource created by Kara Dawson in SD71
A teacher from SD71 has also created an excellent lesson plan for creating Twines - check their stuff out here
To try a story out check out "All Hail the Spider God"
To make your own Twine click on the image below