For "download each chapter of a PDF individually" values of portable non-DIY e-bookness, textbook publisher
DeGruyter does have downloadable versions of its open access books. It's mostly technical science and theology-type things, but there's also some arts & culture like:
Made in Canada, Read in Spain: Essays on the Translation and Circulation of English-Canadian Literature
The
Summer Institute of Linguistics has a very nice set of language and ethnology-related works by their members in PDF format. It's pretty specialized, but they're one of my top resources for certain types of linguistics-related things, including some very useful fonts and software.
For those who are into language learning, they've also an educational project for translating free traditional tales-from-around-the-world storybooks and simple educational factbooks for children into multiple global languages, exportable as PDF (and they plan to have a proper eBook export function eventually), and you can participate (or just download the results) here:
Bloom Library project (
overview of free software for DIY)
Duke Law University's
Center for the Study of the Public Domain only has a few downloadables listed among its publications (a few more can be read online). But they're very topical for MR, and have an excellent and recommended comic book about the public domain, available in multiple languages, along with a few more technical things about IP law, etc..