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.
Simple Contacts - Contact lens prescriptions from home
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.
Kontact - Kontact is the integrated Personal Information Manager of KDE.
FullContact Card Reader - Automagically scan biz cards into LinkedIn/Gmail contacts
EteSync - Secure, end-to-end encrypted and journaled personal information synchronization.