Free Mac program: http://itunes.apple.com/us/app/ibooks-author/id490152466?mt=12&uo=4&at=10l6SU
Free iPad app: http://itunes.apple.com/us/app/itunes-u/id490217893?ls=1&mt=8&uo=4&at=10l6SU
Free iPhone app: http://itunes.apple.com/us/app/itunes-u/id490217893?ls=1&mt=8&uo=4&at=10l6SU
Website: http://www.khanacademy.org/
Free iPad app: https://itunes.apple.com/us/app/id469863705?mt=8&at=10l6SU
Free iPhone app: https://itunes.apple.com/us/app/id469863705?mt=8&at=10l6SU
Free Android Phone app: https://play.google.com/store/apps/details?id=org.khanacademy.android
Free Android Tablet app: https://play.google.com/store/apps/details?id=org.khanacademy.android
Edmodo app: https://spotlight.edmodo.com/product/khan-academy,324527/
Website: http://www.zygotebody.com/