Focus, Relax, Sleep
For the technically inclined, brain.fm's patented method allows for a much larger spectrum of music which in turn provides more stimulation. It's possible to single out instruments in music, modulate them to provide brainwave entrainment, but disguise the modulation as vibrato or tremolo. To the untrained ear, it still sounds very pleasant and yet is still stimulating the brain, and at MUCH higher intensities than binaural beats (binaural beats have a modulation depth of about 3db, significantly smaller than a whisper - see Gerald Oster's paper, 1972).
Now for my experience using it for the past 3-4 months:
I've noticed that when I'm in a focus session I'm able to focus intensely on the task at hand. I've been able to be super productive for hours on end while under the "trance" of these modulated beats. The relax sessions are great for meditation sessions if you're into that. I find that I get into a clear headed meditation state much quicker with the aid of the meditation sessions which are both unguided and guided. I've only done the sleep sessions a few times because I don't have the proper headphones for them (I'll be getting them soon).
If you sign up I believe you get 7 free sessions per week or something along those lines. I signed up for the yearly plan which is $4.99/mo billed annually and cancelled my spotify subscription. I will sometimes play music on youtube with brain.fm in the background which is a nice every once in a while.
All in all, I went into this whole "brain wave entertainment" thing with a skeptical feeling but I'm now a believer in it. There's lots of research being done in this field such as head related transfer functions (HRTFs) which allow for 3D audio and I implore you to look deeper into it if it truly interests you.
Here is a link to the site: https://www.brain.fm/
If you start using it I would love to hear about your experience!