Website: http://www.ck12.org/
Free Android Phone app: https://play.google.com/store/apps/details?id=org.ck12.app.practice
Free Android Tablet app: https://play.google.com/store/apps/details?id=org.ck12.app.practice
Google Chrome app: https://chrome.google.com/webstore/detail/ck-12/ilmbnmigihncgeckjgmkehcgkdeohkhl
Free iPad app: https://itunes.apple.com/us/app/ck-12-free-fun-way-to-learn/id909343639?mt=8&at=10l6SU
Free iPhone app: https://itunes.apple.com/us/app/ck-12-free-fun-way-to-learn/id909343639?mt=8&at=10l6SU
Free iPad app: https://itunes.apple.com/us/app/ibooks/id364709193?mt=8&at=10l6SU
Free iPhone app: https://itunes.apple.com/us/app/ibooks/id364709193?mt=8&at=10l6SU
Free Android Phone app: https://play.google.com/store/apps/details?id=com.amazon.kindle
Free iPad app: https://itunes.apple.com/us/app/kindle-read-books-magazines/id302584613?mt=8&uo=4&at=10l6SU
Free iPhone app: https://itunes.apple.com/us/app/kindle-read-books-magazines/id302584613?mt=8&uo=4&at=10l6SU
Free Mac program: https://itunes.apple.com/us/app/kindle/id405399194?mt=12&uo=4&at=10l6SU
Free Windows program: http://www.amazon.com/gp/kindle/pc
Website: http://www.kno.com/
Free Android Phone app: https://play.google.com/store/apps/details?id=com.kno.textbooks
Free iPad app: http://itunes.apple.com/us/app/textbooks/id424280183??mt=8&uo=4&at=10l6SU
Free iPad app: http://itunes.apple.com/us/app/ted-books/id511071050?ls=1&mt=8&uo=4&at=10l6SU
Free iPhone app: http://itunes.apple.com/us/app/ted-books/id511071050?ls=1&mt=8&uo=4&at=10l6SU
Free iPad app: http://itunes.apple.com/us/app/inkling/id379351586?mt=8&uo=4&at=10l6SU
Website: http://www.chegg.com/
Free Android Phone app: https://play.google.com/store/apps/details?id=com.overdrive.mobile.android.mediaconsole
Free iPad app: https://itunes.apple.com/us/app/overdrive-media-console-library/id366869252?mt=8&uo=4&at=10l6SU
Free iPhone app: https://itunes.apple.com/us/app/overdrive-media-console-library/id366869252?mt=8&uo=4&at=10l6SU
Free Mac program: http://overdrive.com/software/omc/
Free Windows program: http://overdrive.com/software/omc/