This is a collection of tools for maths including both paid and free across multiple platforms
Google Chrome app: https://chrome.google.com/webstore/detail/ahgfknfdplnpiiiiejiimkojdkjlfmdo
Website: https://www.stmath.com/
Free iPad app: https://itunes.apple.com/us/app/st-math-school-version/id550846820?mt=8&at=10l6SU
Free Android Tablet app: https://play.google.com/store/apps/details?id=air.net.mindresearch.stmath
Free iPad app: https://itunes.apple.com/us/app/bigseed/id482245645?mt=8&uo=4&at=10l6SU
Free iPad app: https://itunes.apple.com/us/app/mathpad/id435087400?mt=8&uo=4&at=10l6SU
Paid iPad app: https://itunes.apple.com/us/app/id588713265?mt=8&uo=4&at=10l6SU
Free iPad app: https://itunes.apple.com/us/app/native-numbers-lite-number/id593188849?mt=8&uo=4&at=10l6SU
Paid iPad app: https://itunes.apple.com/us/app/native-numbers-complete-number/id570231808?mt=8&uo=4&at=10l6SU
Paid iPad app: https://itunes.apple.com/app/wolfram-fractions-reference/id538505879?mt=8&uo=4&at=10l6SU
Paid iPhone app: https://itunes.apple.com/app/wolfram-fractions-reference/id538505879?mt=8&uo=4&at=10l6SU
Website: http://mathworld.wolfram.com/
Free iPad app: https://itunes.apple.com/us/app/math-champ-host/id516219390?mt=8&uo=4&at=10l6SU
Free iPad app: https://itunes.apple.com/app/math-champ-client/id516219415?mt=8&uo=4&at=10l6SU
Free iPhone app: https://itunes.apple.com/app/math-champ-client/id516219415?mt=8&uo=4&at=10l6SU