Tag
4 catalogue entries use this topic; each Project's license policy is labeled separately.
Scheduling infrastructure you can host and extend
Cal.com covers the booking link case well, but its real distinction is that scheduling is exposed as infrastructure. Availability, event types, and bookings all have APIs, and the booking page can be embedded rather than linked.
Encrypted email, calendar and contacts with open-source apps
Tuta is an end-to-end encrypted email service with calendar and contacts, offering open-source apps and hosted servers in Germany.
Booking links that read your real availability
Calendly removed an email thread from every meeting anyone arranges with someone outside their company. Share a link, the other person picks from real availability, and both calendars update.