While we're big advocates of pink noise (similar to white noise but with reduced higher frequencies. Think: rainfall and nature sounds), we're also all for binaural beats. Binaural beats are two tones, one in each ear, that are slightly different in frequency. When you're listening to these tones together, your brain processes a beat at the difference of the frequencies.
Binaural beat therapy is used to reduce anxiety and stress and using these sounds can also be beneficial to meditation or improve concentration. In order for this to work properly, you'll need to use headphones to ensure you're receiving different frequencies in each ear and not all binaural beats are for everyone, so experiment with different producers.
If you're interested in trying it out, we've got a beat for when you'd like to find some chill or just focus in on what you're doing. Here's four minutes and six seconds of hang time just for you: