I initially found Brain.fm on ProductHunt when they launched in 2014. The app(only available as a web app at the time for Android) was invaluable to me for both sleep and focus, so when it was offered, I bought a lifetime membership. That may have been a risky purchase because, at the time, the product was young and an app wasn't even available for my phone yet (!!!), but it was the BEST $150 I've ever spent! I love this app and highly recommend it!