PublicAPIs - Explore the largest API directory in the galaxy
Cardhop - The Mac contacts app you'll want to use.
API List - A collective list of APIs. Build something.
Keep In touch - Keep in touch with thousands of people
API for Product Managers - The A to Z of APIs for product managers
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.