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.
Google Calendar - Spend less time managing your day & more time enjoying it
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.
Apple Contacts App - Access and edit your contacts from personal, business, and other accounts with the Contacts app.
FullContact Card Reader - Automagically scan biz cards into LinkedIn/Gmail contacts