Many new iOS app updates are being released today to work with the new iOS 7 on iPhone 4 and later, but one free update expected to draw general interest is a major update to the Amazon Kindle for iOS reader.

The 4.0 Kindle update is optimized for iOS 7, and shares many of the flat design features central to Apple's latest mobile OS. Amazon's description says the design is based on "themes of deference, clarity and depth."

A new Collections feature in 4.0 lets users organize books, documents and magazines more easily. Content can be added to multiple categories.

For example, an Amazon spokeswoman said that "A Game of Thrones" could be categorized in both "My Favorites" and "Fantasy Epics."

Matt Hamblen covers mobile and wireless, smartphones and other handhelds, and wireless networking for Computerworld. Follow Matt on Twitter at @matthamblen or subscribe to Matt's RSS feed. His email address is [email protected].

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