Prototype for BlinkShare

The Muse API is a Java API with the goal of integrating all network-collaboration services into one. The API will give an easy-to-use interface that allows you to log on to multiple services (ie. ICQ, AIM, MSN, Yahoo Messenger, IRC, Napster, Gnutella, Jab

The Google AJAX Search API is an experimental API that lets you integrate a dynamic Google search module into your web pages so your users can mash up Google search results with other content on your site or add search results clippings to their own content.

More tutorials

Ajaxian » Google offers Search, Feed, and Translation APIs to Non Ajax Usage

As a member of the blogging community, I found the advent of APIs to access the various blogging services available to be an incredible boon to the possibilities of those systems.

The update function is used to quickly retrieve an unread count for a given Bloglines account. It requires no authentication.

A URL search allows you to retrieve results for blogs linking to a given base URL. Technorati's cosmos query allows you to specify a wide array of parameters to customize your result set.

Looks like Google reader is working on an API to allow developers to build on top of their data.