Google Calendar

Google Calendar is Google's online calendar, free with a personal account and included in Google Workspace subscriptions. Beyond the individual diary, it handles shared calendars (one per employee, one per truck, one for time off), event invitations, bookable availability slots, and a complete API that other tools use to read and write appointments.

Its role in an automated booking chain is that of source of truth: the AI agent or booking tool doesn't decide availability, it reads it from the calendar and writes confirmed appointments into it. Two bits of craftsmanship for such an integration to work well: one availability calendar (not three calendars contradicting each other), and honest slots that include travel time.