http://blog.stcloudstate.edu/ims/2020/02/04/tophat-and-textbook-publishers/

Top Hat has challenged tangible goods for a long time now. Its first offering was a digital version of clickers to measure student responses in the classroom. In 2017, the company launched a marketplace for e-textbooks, working with authors and offering openly licensed content from the likes of OpenStax as well.

Last year, the company ceased sales of individual assessment tools to instead offer a bundle of its products. Students pay $48 for one year of Top Hat’s products. Interactive textbooks on Top Hat cost an average of $35.

My note: this will be a game changer in regard of the interactivity of textbooks.