What are Brainwaves
Instead of waves of water, brainwaves are electrical, the technique to measure is called EEG. We use to divide the waves to slow and faster waves just like music we have lower sounds and higher sound waves. When you are very focused you might have faster waves called beta and gamma more, when you are more like in a dreamy state you are producing more theta waves. Abnormalities in brainwaves can also indicate some problems in brain health. Healthy brain should go through all brainwave bands everyday [1].
Delta (0 Hz - 4 Hz) Deep sleep.
Theta (4 Hz - 8 Hz) Daydreaming, meditative and hypnotic stages.
Alpha (8 Hz - 12 Hz) This is the relaxation. When we let go of stress and our subconcious mind appears clearer.
Beta (12 Hz - 40 Hz) Daily thinking and activities, stress.
Gamma (40 Hz - 100 Hz) Associated with higher cognitive functioning and so called Aha! moments [2, 3].

What does the app do or what is the brainwave entrainment?
It is the sounds or lights that affect the rhythm or frequencies of the brainwaves. Shamans use to drum around 4 times per second which equals to theta waves range and explains why people have spiritual, meditative etc experiences during these ceremonies.
Similarly the app uses different kind of beats on top of background sounds.

How is this different from some brainwave entrainment I can just listen online?
There isn't much difference. Music when listening from streaming services is sometimes packed but this app uses generators to make sure the sound is right in some cases. This app also randomizes slowly volumes and makes each session have a bit different atmosphere.

Does these things really work? Isn't good music just better?
Lots of studies done on brainwave entrainment and it seems to help with sleep quality [4], alpha waves improve cognition [5] and so on but sometimes these type of entrainments doesn't work well in all areas as expected.
And yes music is also very efficient to our brain, we tend to produce theta waves for example when we listen something we like.

What kind of Brainwave Entrainment is supported and what is the best?
Binaural Beats (These should be listened using headphones)
Monaural Beats
Isochronic Beats
App has also experimental feature which takes any sound for example river sound or wind or whatever and adds mask or effect If you will over it so the sound will have then rhythm using monaural or isochronic beat.
There is no clear evidence supporting any form being best. We prefer monaural beats because of those are soft and comfortable and produce similar effec as other methods.

How to use the app?
Pick session from list and If you want for example to go rest or meditate for awhile set timer to ie 15 minutes and press play. The you can disable the visual flashing and close your phone also what ever feels good or set the visual to be comfortable blinking - this is experimental feature.
NOTE volume doesn't have to be loud at all. There are studies that shows that our brain can recognize these types of stimuli even we don't conciously hear it - hence the sound volume can be something you bearly hear but can also be higher If that is what you want.

App has small advertisement banner that can be removed by buying one time premium pass. Premium also has few other functions or assets more.

REFERENCES (Sry no complete links, no space here enough)
[1] Brain Waves and Sleep Science <> Priyanshi Chauhan and Mohini Preetam Singh
[2] Meditation Gives Brain a Charge, Study Finds <> Marc Kaufman
[3] Aha! in the Brain <> John Kounios and Mark Beeman
[4] Brainwave entrainment for better sleep and post-sleep state of young elite soccer players – A pilot study <> Vera Abeln et al
[5] Alpha brainwave entrainment as a cognitive performance activator <> Victor D. CRUCEANU1, Violeta S. ROTARESCU