Google Calendar: Requirements & High-Level Design

Design a calendar service like Google Calendar for a system design interview — an event row on every calendar it is on, kept in step by a versioned fan-out from an outbox, times kept as local time and IANA zone and recomputed when the rules change, repeating events as RFC 5545 rules, reminders as a queue claimed with SKIP LOCKED, sync tokens, and an estimate from Google's published limits: requirements, estimates, data model, API and high-level design.