Kindle

As of this writing, the Kindle Store lists 5,902,458 different titles. 

If Amazon wanted to, it could with a single act bring a new form of book into being. That's because Amazon has more or less vertically integrated the entire book industry within its walls, building a complete reading universe of its own making. Lots of authors now write books especially for Amazon, which readers find on Kindle Unlimited and Prime Reading, read on their phone and tablet, listen to through Audible or your Echo, and then talk about on Goodreads. Amazon has tools that help you write your book, format the manuscript, design the cover, file the right metadata, publish to the right places, and get paid the right amount. Want to make a comic book, a kids' book, or a textbook instead? Amazon can help there too.

https://www.wired.com/story/can-amazon-change-books/

Everyman his own historian.  (by Carl Becker)