6. MCGRAW-HILL SMARTBOOKS
You had to know the publishing giants would make their presence known beyond a single platform, and McGraw-Hill Education’s Smartbooks are no exception. The $19.99 reader-adaptive digital textbooks capable of measuring everything from retention to reading pace are available on Android tablets as well as the iPad. As of CES 2013 in January, they were also considering a Windows 8/RT version.