Melange
A photographer needs a model. A model needs a stylist. Right now that happens in Instagram DMs. I built an app for it, and shipped it on both iPhone and the web.
How it works
Post what you're working on. Swipe through other people's projects. When you both say yes, a chat opens and you plan the shoot.
The interesting engineering
Most apps have a server in the middle that decides what each user is allowed to see. This one doesn't. The iPhone app and the website both talk to the database directly.
That's only safe if the database itself knows the rules — so that's where I put them. Every table checks who is asking before it returns anything.
No. The app can ask, but the database checks who you are and returns nothing at all.
The payoff: a bug in either app can't leak private messages, and a third app added later inherits the same guarantees for free.
What's built
Everything above works on both the phone and the web, on one shared account. Thirty automated tests run on every change.
Where it stands: the app builds and the submission pipeline works, but it isn't in the App Store yet — screenshots are the main thing missing.