The Phone app best considered for enhancing the ear musically

Is there a software best useful to a singer for the training of the ear musically? Can one get a software that is best useful to the Android OS and iPhone OS phones? For a couple of days now I have been in need of an application software that can assist me in training my amateur singers more especially their hearing ability as upcoming musicians. It has become much of a pressing need to me and therefore hope to get the needed assistance in my quest for such app. Thank you.