SOGo - SOGo is groupware server with a focus on scalability and open standards.
FareHarbor - Reservation software for activity and tourism businesses. Low credit card processing rates, mobile friendly. Built for you.
Baïkal - Cal and CardDAV server
Xola - Xola is an elegant and powerful online booking and distribution system. We help tour and activity providers reduce costs, grow revenue, and save time.
Xandikos - Lightweight CalDAV/CardDAV server on top of Git.
TrekkSoft - The website builder and booking solution for tour operators and activity providers