I built SleepSoundMixer after struggling with sleep and focus. It’s a browser-based tool — no install, no sign-up — where you can layer 40+ synthesized ambient sounds like rain, fireplace, brown noise, and birdsong into your own mix. There’s also an AI mode that reads your mood and builds a soundscape for you, a 4-7-8 breathing guide, and a Pomodoro timer built in. Free to use. Works on any device. Headphones recommended.