Binaural Sound Central allows you to meditate and relax with true Binaural Beats. These beats are made by putting 2 distinct separate sine waves or pitches in each year. The interference of the two frequencies is what your brain makes into a binaural beat. To use this app and get the full effect you have to use earbuds/headphones to get the discrete sounds to each ear.
Gamma - Higher brain activity, Problem Solving
Beta - Active, Busy Thinking, Active Concentration
Alpha - Relaxation
Theta - Dreams, Deep Meditation, REM Sleep
Delta - Deep dreamless sleep