We built Hotly, an inbox where people pay to send someone a note and that person replies when they have time. It started as a product for one creator whose DMs had become unmanageable. This month we open-sourced it under Apache 2.0, so anyone can run their own. This isn't a launch post. It's the handful of decisions that shaped the code, and why we made them. 1. One person per install The obvious design is multi-tenant: one database, many creators, a creator_id on every row....