The FuseMail PHP SDK by Nikhil Gupta integrates email hosting services by interacting with the API. Documentation available at https://www.fusemail.com/support/api-documentation/
Bitcoin point-of-sale specialist Coinkite has released a Tor bitcoin wallet API as they look to encourage privacy-conscious web solutions for the bitcoin ecosystem.
Google, in what appears to be a new initiative to make their APIs more secure for end users and easier to for developers to work with, has begun rolling out OAuth 2.0 support for its APIs. This brings about two major changes in how apps integrate with Google APIs.