I built Genvap, a browser-based tool that takes a screen-shot or recording and renders it onto a real 3D device (phone/laptop), with camera animations, backdrops, and text overlays, then exports up to 4K.

I make a lot of small apps and kept running into the same problem: every App Store preview / demo video tool wanted a monthly subscription for something I'd use a handful of times a year. So Genvap is pay-per-export instead — $0.99 for an image, $4.99 for a video, nothing when you're not using it.

Stack: Next.js, Three.js for the 3D rendering, GSAP for the camera animation sequencing, Firebase, Stripe for one-off payments.

Happy to answer questions about the 3D rendering approach or the pricing model — genuinely curious whether pay-per-use lands better than subscription for a tool like this.