Micro-blogging website Twitter has been one of those rare true internet success stories since it launched back in 2006, with the site joining the likes of Facebook, Google and YouTube in becoming household names.

The site is still continuing to grow, with the company announcing in a blog post yesterday that there are now more than a million registered Twitter apps available online. This is up from just 150 000 apps a year ago, with the site claiming that a new app is registered every 1.5 seconds.

Some 750 000 developers from around the globe has contributed to this phenomenal growth, with the company announcing that some $500 million has been invested into the Twitter ecosystem since December 2010.

Many may not be familiar with what exactly Twitter apps are, having only used the site in its plain micro-blogging format. Examples of some of the apps available include Mass Relevance, an app which combed through 160 000 tweets to organise the US White House's first Twitter Town Hall meeting, with ordinary Twitter users debating and discussing issues with government representatives.

Trendr is an app which can evaluate how people feel towards a certain product by analysing tweet content, with the app successfully used to measure the response to sci-fi thriller film SUPER8 after its blockbuster $38 million opening weekend.

More apps includes Poptweets, an iPhone trivia game where users match up celebrity tweets, and Radian6, a brand monitoring tool recently acquired for the tune of $326 million.

In addition to announcing its impressive app milestone, Twitter also introduced a new Twitter Developer site. Through the developer site, “anyone in the ecosystem can start building with Twitter, connect directly with Twitter team members, exchange ideas with fellow developers, and find all the resources they need to create their own product or business.”