How do I schedule across companies without sharing calendars or creating accounts?

Inside a tenant, free/busy is a directory feature: the calendar server already holds everyone's data and can answer “is Ana free at 3pm?” without disclosing what Ana is doing. Across tenants there is no shared directory and no shared trust, and the protocols that could bridge them require deliberate admin configuration on both sides.

The result is familiar: the moment a meeting involves two companies, scheduling reverts to email. That is not a tooling oversight — it is the boundary working as designed. The question is what to put on top of it.

Propose candidate times, share a link, let everyone mark what works. Doodle popularised this; Lucie Sync group events do it too.

Good for: groups, especially when participants have no shared tooling and some have no account anywhere. Nobody reveals a calendar; they reveal opinions about specific times.

Costs:a full round-trip of human attention. Every participant must open the link and respond, and the poll stalls on whoever is slowest. Proposed times can also go stale — the organiser's own availability may change while voting is open.

One person publishes their open slots at a stable URL; the other picks one and it books itself. Calendly, Cal.com and Lucie Sync booking pages all work this way.

Good for:one-to-one meetings where one side's time is the constraint. It collapses the round-trip to a single action by one person.

Costs:asymmetry. It works because one party's availability is authoritative and the other fits around it, which reads as presumptuous between peers and does not extend cleanly past two people — three booking links do not intersect themselves.

The same open slots as a booking link, but returned in a form software can consume — so an assistant can read several people's availability, intersect it, and book the overlap without anyone opening a page.

Good for: removing the round-trip entirely, and for groups, since intersecting three endpoints is a computation rather than three more conversations.

Costs: everyone whose availability is being read needs such an endpoint. This is the newest pattern and the least universally supported — in practice it means the participants share a tool that offers it.

• Mixed group, no shared tooling — a poll. It is the only pattern that works when some participants have nothing installed and no account.
• One-to-one, asymmetric — a booking link. Fewest moving parts.
• Recurring cross-company scheduling between peers — availability endpoints, if the people you schedule with most often have them.

Lucie Sync offers all three against one handle: a poll for people with no account, a booking page for humans, and an MCP endpoint for assistants — with the same guarantee across all of them, that only open slots are ever disclosed. It supports Google Calendar only, so Outlook-based participants need one of the first two patterns. It also isn't something you adopt on its own: it comes with a Lucie Network membership, which is the point of the model — the people you most often need time with are already in the room.