Last September I started writing a Freshman Physics book, based on the course I had given for many years. Writing was actually quite straightforward. I opened my notes, and, instead of talking, I typed. I had always composed my own homework problems, so those could simply be cut and pasted into the book at the right places. Typing out the worked solutions to some of the problems was a bit of a chore. A second writing pass inserted the Figures (I may add more in the third pass.) For the very simple figures I would — before I retired — put on the blackboard, I used Inkscape to create the needed circles and lines.
The book is novel in that: It is calculus-based from the beginning. Students are assumed to know simple integrals and derivatives before the book starts. Space is consistently treated as being three- rather than two-dimensional. As a result, angular momentum is consistently treated as being a vector quantity.
The radical innovation will be price. Thanks to modern advances in publishing, I anticipate that the book will sell for $20 rather than $300. The importance of that number has increased substantially since I began writing. I expect to finish the refined rough draft this month.