A book is a written work typically longer than an article, on the indieweb, there are examples of publishing whole books on IndieWeb sites, and publishing lists of books.
Jeremy Keith publishes books on his own personal domains in addition to through publishers. E.g.
In 2009, Kathleen Fitzpatrick released Planned Obsolescence in draft form for open peer review in fall 2009 (she was an editor on the site). It was later published in physical form by NYU Press in 2011, but the original with annotations is still available online.
The mobile app version of Pocket has a "page flip" functionality which allows readers to swipe left/right as if they were reading their articles in e-book format rather than the traditional up/down scrolling UI typical of most browsing experiences.
Below are some examples of people keeping lists online of books they own, see also personal library for more examples:
Erin Jo Richey
Has a page on her site with books she owns: http://erinjorichey.com/library/
Has a page with a few books he knows (either owns/owned or borrowed or read or want to read) on https://seblog.nl/bieb