I am creating a textbook in InDesign. It is free, online, and covered by a Creative Commons license. Currently, I'm publishing PDFs designed to be printed and then read, with a two-column primary text frame to make the printed line length short for readability.
But PDFs suck for reading online, particularly if you're trying to do so on a tablet or your phone. Plain-vanilla HTML is not too bad for this, but then there are problems dealing with graphics, cross-references, footnotes, sidebars and the like. "Publish online," in my mind, is inferior to posting a PDF.
I considered trying to make a Kindle book, but that's no good for something free, online and under a Creative Commons license. Other eBook formats are not so widely used.
WordPress is not bad for this, if you use a theme or an add-on that mobilizes the site. This is especially so as WordPress makes it easy to change big graphics to small thumbnails. Clicking on these thumbnails lets you see the graphic full-size, which may be needed for big textbook illustrations.
I suppose I could copy the text into WordPress, with each section being a page or post, and pasting in the graphics. However, this loses some InDesign features such as cross-references and the like. And it's a lot of work. And it's a lot more work to keep up to date as I update the original document.
Now that In5 is including a responsive-design output/layout, I am thinking about doing In5. However, there is still the problem of viewing graphics on a phone, especially some of the full-page graphics that will require zooming and panning on a phone or small tablet.
I would be very interested to hear some opinions from the experts on this forum who have been so helpful to me and others in other posts.