PressBooks lets you and your team easily author and output books in multiple formats including: epub, Kindle, print-on-demand-ready PDF, HTML, and inDesign-ready XML.

A great solution would be a service or plugin that categorizes everything based on reading time. At the most basic level, this would be calculated by the word count. There are already a number of plugins for WordPress that accomplish this1, and it can be done with less than 10 lines of PHP.

Create a tumblr style blog using this plugin.

Use the power of WordPress to transform online content into an electronic book.