I’m surprised I haven’t read about Sutori before. Sutori is based around its concept of stories. A Sutori story is a lesson that can be displayed as a web page or as a presentation. What’s cool is that you can plan out the lesson with activities and information for students, and automatically have a slide show that you can use in the classroom to present the lesson.
They have a free tier, which is pretty limited. Pricing starts at $99/year per teacher, or $2,500 for a school.