Show HN: Rainlayer: Authentic 3D rain audio app with Metal-rendered BG

Hey HN,

I've been working on Rainlayer, a focus and sleep app built around authentic binaural 3D rain recordings. After a few weeks live, it's doing well in the US (3.7% conversion rate) and I'm looking for feedback, especially from founders who might be my target audience.

The backstory: I previously built the weather app Haze (2013) and Thunderspace (2014), both featuring a distinctive background effect rendered in OpenGL ES. For Rainlayer, I wanted to recreate that visual experience but modernized, in a semi-holographic way.

AI tools helped me port the rendering pipeline from OpenGL ES to Metal, which was a non-trivial process that probably would have taken me 10x longer. I used mostly NotebookLM for research and Windsurf for accelerated engineering, along with some custom-built CLIs that helped me craft specs more easily.

What makes Rainlayer different: All audio is genuine binaural 3D recorded from nature. There's no AI-generated content, no synthetic samples. I deliberately avoided gen AI here because I believe authenticity will become increasingly rare. The explorable sound field is designed without traditional "tracks", in a way that you get harmonious, natural transitions.

I'm particularly interested in feedback from startup founders who work under extreme pressure and who appreciate quality. My hypothesis is that founders dealing with constant context switching and decision fatigue might find this valuable, but I'm still validating that assumption. What features would make a focus/sleep tool more valuable to you?

The app is live on the App Store and you can try it without barriers. I haven't cracked distribution yet. This post is part of figuring that out, and I appreciate any pointers you might have.

What do you think? Open to any kind of constructive feedback.

Cheers, Franz