SOGo - SOGo is groupware server with a focus on scalability and open standards.
Rezdy - Tour operators in 73 countries use Rezdy's booking software to sell thousands of products in real-time on their website and through distribution channels.
Baïkal - Cal and CardDAV server
Eventric - Eventric is an professional tour management solution.
Xandikos - Lightweight CalDAV/CardDAV server on top of Git.
Zentrumhub - One Integration That Expands your Business