Peek Pro - Peek Pro is a fastest growing appointment scheduling software specially designed for tours and activity operators to help increase their booking reaching out to large numbers of potential customers, mostly tourists.
Baïkal - Cal and CardDAV server
Eventric - Eventric is an professional tour management solution.
Radicale - The Radicale Project is a complete CalDAV (calendar) and CardDAV (contact) server solution.
FareHarbor - Reservation software for activity and tourism businesses. Low credit card processing rates, mobile friendly. Built for you.
SOGo - SOGo is groupware server with a focus on scalability and open standards.