My brain is fogged. Cognition dubious. I'm digging into the possibilities pile. This application has been out for a while now. Adobe Story Free allows you to create and work on scripts any place and any time with an Internet connection.
This is an overview video of the software by Karl Soule:
This is more than I need in putting together a script but one module did get my interest. The multi-column script feature would be a good match for me. I do like putting images and other media in a script to visually remind me of the structure of what I want to accomplish.
I can see it being useful for tutorial type projects than free flowing. I would take a look at the Adobe Help page for Story to get a glimmer if this would be of interest to you
Anyway, it is free with Adobe registration. If you have a consistent Internet connection and a willing mobile device you might want to give this a look.