In my new mini-book I used a new (to me) fun process. The process I am referring to as agile writing, is based on the best low-pain tools I could find. It would not be unfair to say I wrote a minimum viable book (MVB). The tools are mainly google docs, limnu drawings, and screen captures of vim with auto-coloring. The code was super-easy because vim auto-coloring works really well IMO:
Note that google docs has a nice crop interface so you don't need to screen capture precisely.
The white-boarding in limnu took me a little getting used to, but works very well. Here's an example of a screenshot from limnu pasted into google docs:
They wrote up the advice at their site.