fruux - Free service that takes care of your contacts, calendars and more so you don't have to.
Flexibits - Makers of Cardhop, Chatology, and Fantastical.
FullContact - Put the power of full contact information into your web or mobile apps.
Apple Contacts App - Access and edit your contacts from personal, business, and other accounts with the Contacts app.
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.
Kin - Kin is money for the digital world. It is used to generate value through a shared, decentralized cryptocurrency in a digital ecosystem of apps and their users.