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.
Nextcloud Contacts - The Nextcloud contacts app is a user interface for Nextcloud's CardDAV server.
Drupe - Next generation contact manager and dialer.
Microsoft People - People in Windows 10 puts all the ways you connect with all your friends, family, colleagues, and acquaintances in one place, so it’s faster than ever to keep in touch.
Simple Contacts - Contact lens prescriptions from home
Kontact - Kontact is the integrated Personal Information Manager of KDE.