Yahoo has launched a new Contacts API, which uses OAuth. With the API, applications can allow users to read, write, and sync access to their Yahoo Address Book, which is one of the biggest address books on the web.
"We've completely reengineered the existing Contacts API and added more useful functionality for developers," says Yahoo Social Platforms Product Manager Shirish Anand.
Google has recently launched a standalone contacts manager, which lets you manage your contacts outside of Gmail. This would be particularly useful for those who don't use Gmail, but use other Google products that offer sharing capabilities.
If you use Google Docs, Picasa, or Google Calendar for example, you can now update people's contact information without having to use Gmail. This was not an option before.