Reservations are written inside serializable ACID transactions (Convex) against a derived per-night occupancy table. Two guests can't take the same night, even clicking Pay at the same instant.
Seasonal rates, min/max stay, lead time, booking windows, prep/turnover buffer nights, deposits (full / percent / flat / first-night), time-windowed cancellation policies, taxable and non-taxable add-ons.
Every unit gets a secret-token .ics feed, so direct-listed Airbnb calendars and legacy PMS bridges stay in sync.
No SaaS — each operator runs their own Convex deployment. Free tiers get you to ~$0/month, and self-hosting is possible with the open-source convex-backend if you want everything on your own infrastructure.