Apps to CardDAV

Google Sync was a free service offered by Google to synchronize mail, contacts, and calendar data across multiple devices and platforms. It leveraged various protocols like Exchange ActiveSync, CardDAV, and CalDAV to push updates in real-time, ensuring users had consistent information wherever they accessed it.

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.

Business Calendar is a robust and feature-rich calendar application designed specifically for users who need a powerful and organized way to manage their schedules, events, and tasks. It offers a clear overview of appointments, integrated task management, and extensive customization options to cater to demanding professional needs.

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.

Jorte is a comprehensive calendar and organizer application designed to help users manage their schedules, tasks, and notes efficiently across multiple devices. It offers a flexible and customizable interface to suit individual preferences and integrates with popular calendar services.

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.