InkleWriter

Inklewriter Free is openware and may be a stretch for Grade 3. The site has a great example of what an interactive story is by presenting it as a tutorial!

Inklewriter Free keeps track of the missing story threads. As you went down the path of a particular story thread, it prompts to lead you back to the beginning of the story or the fork for the next thread, as well as prompts to see if it could connect to a similar point on another thread.

Inklewriter Free takes care of the links to the next thread, something that would be time consuming for the students to do, and make sure they do correctly.

Overall, this could be a good fit for a Grade 3 class, but it would need to be something that was taught over several months, beginning with the story creating. On a teaching level, this program has only one use, whereas other tools, such as Google Slides or Book Creator, would be using and improving skills the students already have.