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
Truecaller - Find a person by a name or phone number worldwide for free using Truecaller.
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
Kontact - Kontact is the integrated Personal Information Manager of KDE.