Here’s a very simple idea: Use Project Gutenberg for content and Readability for style.
Project Gutenberg has a large collection of public domain books in digital form. The books are available in several formats, none of which are ideal for reading. Project Gutenberg provides text without much styling in order to make it easier for people to use the content as they please.
You can go to the HTML version of a book on Gutenberg and use Readability (or Instapaper) to format it for easier reading. Importing the HTML page to a Kindle similarly improves the formatting.
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Has anyone made a style sheet to approximate the look of Readability or Instapaper? I’d like to use something like that to improve the appearance of the static HTML pages on my site.