These are some apps I found useful
Paid iPad app: https://itunes.apple.com/us/app/history-ib-cold-war/id837813901?mt=8&uo=4&at=10l6SU
Paid iPhone app: https://itunes.apple.com/us/app/history-ib-cold-war/id837813901?mt=8&uo=4&at=10l6SU
Paid iPad app: http://itunes.apple.com/app/barefoot-world-atlas/id489221652?ls=1&mt=8&uo=4&at=10l6SU
Free iPad app: https://itunes.apple.com/us/app/mycongress/id364897048?mt=8&uo=4&at=10l6SU
Free iPad app: https://itunes.apple.com/us/app/early-jamestown/id395229194?mt=8&uo=4&at=10l6SU
Free iPad app: https://itunes.apple.com/us/app/mahjong-usa/id883486908?mt=8&uo=4&at=10l6SU
Free iPhone app: https://itunes.apple.com/us/app/mahjong-usa/id883486908?mt=8&uo=4&at=10l6SU
Free iPad app: https://itunes.apple.com/us/app/world-book-this-day-in-history/id364739528?mt=8&uo=4&at=10l6SU
Free iPad app: https://itunes.apple.com/au/app/stack-the-countries-lite/id407838751?mt=8&uo=4&at=10l6SU
Paid iPad app: https://itunes.apple.com/us/app/stack-the-countries/id407838198?mt=8&uo=4&at=10l6SU
Free iPhone app: https://itunes.apple.com/au/app/stack-the-countries-lite/id407838751?mt=8&uo=4&at=10l6SU
Paid iPhone app: https://itunes.apple.com/us/app/stack-the-countries/id407838198?mt=8&uo=4&at=10l6SU
Paid iPad app: https://itunes.apple.com/app/wolfram-us-presidents-reference/id461930662?mt=8&uo=4&at=10l6SU
Paid iPhone app: https://itunes.apple.com/app/wolfram-us-presidents-reference/id461930662?mt=8&uo=4&at=10l6SU
Free iPad app: http://itunes.apple.com/us/app/imf-news-and-data-for-the-ipad/id414587764?mt=8&uo=4&at=10l6SU
Paid iPad app: https://itunes.apple.com/us/app/learn-money-counting-coins/id579562378?mt=8&uo=4&at=10l6SU
Paid iPad app: https://itunes.apple.com/us/app/discovery-exploration-maps/id420897293?mt=8&uo=4&at=10l6SU
Paid iPad app: https://itunes.apple.com/us/app/montessori-approach-to-geography/id445130629?mt=8&uo=4&at=10l6SU
Paid iPad app: https://itunes.apple.com/us/app/united-states-america-montessori/id404405760?mt=8&uo=4&at=10l6SU
Paid iPhone app: https://itunes.apple.com/us/app/united-states-america-montessori/id404405760?mt=8&uo=4&at=10l6SU
Paid iPad app: https://itunes.apple.com/us/app/virtual-history-roma/id410358487?mt=8&uo=4&at=10l6SU
Free iPad app: https://itunes.apple.com/us/app/ilearn-us-states-lite-version/id604698643?mt=8&uo=4&at=10l6SU
Paid iPad app: https://itunes.apple.com/us/app/ilearn-us-states/id480219484?mt=8&uo=4&at=10l6SU
Free iPhone app: https://itunes.apple.com/us/app/ilearn-us-states-lite-version/id604698643?mt=8&uo=4&at=10l6SU
Paid iPhone app: https://itunes.apple.com/us/app/ilearn-us-states/id480219484?mt=8&uo=4&at=10l6SU
Paid iPad app: http://itunes.apple.com/us/app/britannica-kids-us-presidents/id477792298?mt=8&uo=4&at=10l6SU
Paid iPhone app: http://itunes.apple.com/us/app/britannica-kids-us-presidents/id477792298?mt=8&uo=4&at=10l6SU
Paid iPad app: https://itunes.apple.com/us/app/modern-world-history-gcse/id807467139?mt=8&uo=4&at=10l6SU
Paid iPhone app: https://itunes.apple.com/us/app/modern-world-history-gcse/id807467139?mt=8&uo=4&at=10l6SU
Free iPad app: https://itunes.apple.com/us/app/constitution-for-ipad/id363287472?mt=8&uo=4&at=10l6SU
Paid iPad app: http://itunes.apple.com/us/app/stack-the-states/id381342267?mt=8&uo=4&at=10l6SU
Paid iPhone app: http://itunes.apple.com/us/app/stack-the-states/id381342267?mt=8&uo=4&at=10l6SU
Website: http://www.youtube.com/teachers
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/
Paid iPad app: http://itunes.apple.com/us/app/britannica-kids-ancient-rome/id424128583?mt=8&uo=4&at=10l6SU
Paid iPhone app: http://itunes.apple.com/us/app/britannica-kids-ancient-rome/id424128583?mt=8&uo=4&at=10l6SU
Free iPad app: https://itunes.apple.com/us/app/ilearn-continents-oceans/id481545907?mt=8&uo=4&at=10l6SU
Free iPhone app: https://itunes.apple.com/us/app/ilearn-continents-oceans/id481545907?mt=8&uo=4&at=10l6SU
Paid iPad app: https://itunes.apple.com/us/app/timeline-civil-war/id680553239?mt=8&uo=4&at=10l6SU