Blinkist - Key insights from 6,000+ bestselling books and podcasts
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Littler Books - Concise book summaries of essential nonfiction
SparkNotes - SparkNotes is a resource that provided study guides for multiple different types of subjects.
Book Summaries - Great books summarized in 5 quotes (or less) so you can get the main idea fast.
12min APP - Free reading app for summaries of nonfiction books.