Cross-site activity stream aggregator FriendFeed has answered the loud calls of users and developers and today released the first version of its Application Programming Interface, or API. The FriendFeed experience will now be accessible on platforms outside of the web page and FriendFeed user data should have all kinds of interesting things done with it.

FriendFeed is the new hotness and many people have asked for an API to take the service to the next level. There aren't any example apps built yet, nor has there been much developer feedback yet. A whole lot of things just became possible, though.

As for technical details: FriendFeed is first releasing Python and PHP libraries, there's an undisclosed access limit and oAuth authentication is "coming soon" (we hope so).

If you're less than on fire about APIs and their potential - check out our post called APIs and Developer Platforms, A Discussion of the Pros and Cons - and know that 16 of the 18 authorities quoted in that post were interviewed entirely through a 3rd party Twitter client using that API.

If you're a Twitter user you know how essential to Twitter that company's API has become, an estimated 80% or more of Twitter use comes in through the API and the constellation of 3rd party services that leverage it. The FriendFeed API may be the most eagerly awaited since Twitter's.

This Aint Just RSS Readin'

Casual users should take note that FriendFeed is far more than just an RSS aggregator. Check out the podcast and transcript of our interview with the company's founders in early February for details. See also my recent interview with RSS keystone Dave Winer, where we discussed FriendFeed more than anything else. You'd have seen it already if you were my friend on FriendFeed.

Commenting, feed and item display, liked-by-a-friend item exposure and a smooth friend recommendation path are some of the key differentiators of FriendFeed. In February at least, only 70% of the feeds coming into FF were RSS feeds, too. The rest are from other kinds of 3rd party APIs that the FriendFeed team has tied into by hand. There are many different Lifestreaming apps, but FriendFeed has a lot of momentum, a good user experience, renders well on mobile and has caught peoples' imaginations. It's also got some heavyweight backers.

The Possibilities

Some of the examples from the FriendFeed announcement are these:
"[The API is] designed to make it possible for anyone to improve FriendFeed or integrate FriendFeed into other applications. You can develop a FriendFeed interface for a mobile phone, build a FriendFeed widget for your blog, or develop an application that makes it easy to post photos to your feed from your iPhone."

I'm cheering for an Adobe AIR desktop interface, APML import/export and some sophisticated item-level recommendations. How about a FriendFeed/Imeem mashup? I'd love to listen to a streaming radio station of all the music that my FriendFeed friends favorite on their respective music networks. Oh the possibilities are many. This is a very exciting announcement.