How a video meeting platform models its data: accounts and assigned licences, a meeting series separated from its materialised occurrences, registrations, participant join and leave intervals, breakout rooms, recordings, in-meeting chat and waiting room admissions.
How a calendar app models its data: calendars and sharing, events with their own time zones, RRULE recurrence with exception dates and per-occurrence overrides, attendees and RSVP, reminders, working hours and a free-busy index.
How a community chat platform models its data: servers with nested channels, roles carrying permission bitfields, three-state per-channel overwrites, per-server nicknames, messages and threads, reactions, attachments, invites and voice sessions.
How a webmail service models its data: labels applied many-to-many instead of IMAP folders, one stored copy per message, conversation threading, attachments deduplicated by content hash, delivery filters, drafts, read state, spam scoring and quota.
The phpBB and Discourse shape rather than the Reddit one: curated categories and boards, threads bumped by replies, flat numbered posts with quoting, reputation and badges, a report-driven moderation queue and private messages.