Kontact - Kontact is the integrated Personal Information Manager of KDE.
Lightning Calendar - Organize your life — it’s about time!
Nextcloud Contacts - The Nextcloud contacts app is a user interface for Nextcloud's CardDAV server.
Simple Calendar - A simple calendar with events (optional recurring and reminders), week numbers and a customizable...
Google Contacts - Google Contacts is Google's contact management tool that is available in its free email service Gmail, as a standalone service, and as a part of Google's business-oriented suite of web apps Google Apps.
Google Calendar - Spend less time managing your day & more time enjoying it