Websites to CardDAV

Plaxo is a comprehensive online address book and contact management service designed to keep your contacts organized, synchronized, and up-to-date across various devices and platforms. It offers robust features for merging duplicates, integrating with popular services, and providing a unified view of your network.

Microsoft Exchange Server is a robust mail and calendaring server designed for businesses of all sizes, providing enterprise-grade email, calendaring, and contact management capabilities.

fruux is a robust cross-platform synchronization service designed to keep your contacts, calendars, and tasks seamlessly in sync across all your devices and applications. It offers a secure and reliable cloud platform with strong privacy focus, ideal for individuals and teams needing consistent data access and collaboration.

Horde Groupware is a free, web-based suite of applications designed for collaboration and productivity. Built on the robust Horde framework, it offers a comprehensive set of tools including webmail, calendar, task management, and note-taking, providing an integrated platform for individuals and teams.

Zimbra Collaboration Suite is a comprehensive open source email and collaboration platform designed for businesses. It provides a secure and feature-rich environment for email, calendaring, contacts, tasks, and file sharing, supporting on-premises and cloud deployments.

Nylas Mail, an extensible open-source email client, offers a unified inbox, robust search, and calendar integration. It supports multiple accounts and provides features like email tracking and undo send, aiming to enhance productivity and email management for users.

Kolab Community is a comprehensive, free, and open-source groupware suite designed for collaborative work. It provides integrated email, calendar, contacts, and tasks functionalities, empowering individuals and teams to communicate and manage their data efficiently and with a strong focus on data privacy.