You take bookings by phone or chat and keep the overview in your head or a spreadsheet. I build a booking system that shows free slots, takes a booking, blocks double bookings and lets the customer cancel with a link until a deadline you set. Time zones and the switch to winter time are handled. Before delivery the system runs through automated tests, including twelve booking attempts on the same slot at once, of which exactly one may succeed. You get the source code, a setup guide and the test suite, and you run it on your own server or hosting.