For a long while, Stanza was the iPhone’s answer to the Amazon Kindle. The free ebook program became one of Apple’s more popular apps by allowing users to tap into 100,000 books and periodicals.

This purchase shows Amazon’s commitment to digital books, a market that it dove into in 2007 with the $399 Kindle e-reader. The online retailer pushed deeper with a $50 price drop, second-edition hardware, expanded library of e-book titles, its own Kindle app for the iPhone, and now the acquisition of Stanza.