Baïkal - Cal and CardDAV server
BookSteam - BookSteam Online booking and appointment scheduling software for businesses worldwide. Easy to use, cloud based web scheduler that includes class and group bookings. Calendar management and schedule organization, trusted by thousands.
SOGo - SOGo is groupware server with a focus on scalability and open standards.
Acuity Scheduling - Automate your client bookings, cancellations, reminders & payments using the worlds friendliest online scheduling software.
Xandikos - Lightweight CalDAV/CardDAV server on top of Git.
MINDBODY - Find and book fitness and beauty classes near you.