Binaural frequencies 
(these frequencies can overlap a bit depending on the literature that you are reading)

You have two sine waves made of slightly different frequencies to form a desidred frequency difference. The tone produced can alter the type of brain activity a person experiences. The change to the brain's electrical patterns can then be used to enhance many aspects of a person's physiological and physical state.

< 4 Hz Delta wave - Sleep without REM
4-7 Hz Theta - Dreaming, profound meditation, sleep with REM
7-13 Hz Alpha - Relaxed but active
13-38 Hz Beta - Activity, good concentration
40 Hz Gamma - most recent studies have focused on the 40Hz with interesting results
40.5 Hz Gamma to 50 Hz - better than morning coffee

There are many apps on Android and ios to choose from.