App, it contains most of the common Buddhist prayers which support audio. You can use it if you forget to bring your prayer book, just keep it in your phone and you can use it anytime, anywhere. Some of the prayers included are the daily prayers that we chant in schools, or special occasions.
Since these prayers are for Buddhist people specially Tibetans, therefore the default language is in Tibetan. Please do share among your friends and family.
 
The function of a mantra is understood differently by the several schools of Buddhism, but at its most basic level, the chanting of a mantra is thought to evoke enlightenment. Sometimes mantras are used as a form of meditation.