The Twitter API (Application Programming Interface), opens up the data and functionality of the social media behemoth to third party developers. The number of applications powered by it is huge; clients for mobile phones and computers such Tweetdeck, Seesmic and Twidroyd, online media posting sites like Posterous and TwitPic, stats mashups like TweetStats, blog commenting software with twitter integration such as IntenseDebate, online tools for power tweeters like Hootsuite, the list goes on.

The recent launch of Twitter's own @Anywhere interface to the API makes it even easier for site owners to twitterize their websites.

The Twitter API could just be the most significant piece of software development of the decade. Although twitter.com is still the most popular way of tweeting, if Twitter had been just a website, with no API, no extended reach, no innovative interfaces, would it have been as successful? I don't think so.