IGI global book chapters
IGI Global allows authors to publish book chapters for free, with the potential for journals to generate revenue later on. It's worth mentioning that IGI Global offers a robust editorial system for researchers keen on writing a book. Additionally, they assist in marketing the book. Nonetheless, a drawback of this publishing model is that it's not open access.
example book chapter:
https://www.igi-global.com/chapter/rethinking-the-publish-or-do-not-graduate-paradigm/345639