On a related note, they've offered other services over the years. In the early years Feedbooks also let you build an ebook from a collection of RSS feeds. The Kindle and PDF formats (this was before Epub) even included a link so you could download an updated ebook. At one point Feedbooks also offered a Kindle download guide. This was a collection of book listings for all the Kindle format ebooks available via Feedbooks. You could load this on to your Kindle and then directly download any ebook you wanted to read. The Kindle download guide persisted into 2010, and it was retired only when Amazon made it technically difficult to maintain (frequent unexplained changes, I'm told).
Feedbooks sees around 3.5 million downloads a month, putting it somewhere behind Project Gutenberg's 4.9 million. Epub is the most popular format, and iOS and Android are the most popular formats.