Facebook, the number three social networking site in the UK is hoping to spring board itself into the number one position ahead of Bebo and MySpace by encouraging other companies to sell products and create software for use on the site.

The move, the first for a social networking site, is hoping for a similar response when Bill Gates took the same approach with Microsoft.

"Until now, social networks have been closed platforms", Zuckerberg told about 750 programmers attending the company's first developer conference, dubbed f8. "We're going to end that."

Zuckerberg introduced the new markup language, Facebook Markup, which along with its previously released APIs allows developers to build applications fully integrated into the site.

Facebook Markup includes features, such as dynamic information tags, conditional privacy tags, image caching and Flash.

The aim is that developers will be able to build anything they want in full, unlimited application pages on Facebook, called the “canvas pages”, and applications also can have a box in users’ profiles and navigation.

The Palo Alto-based startup has so far recruited about 65 companies to create software for the Facebook Platform, which has been opened up to any company wanting to get involved.

Applications within profiles will remain free of advertising, but Facebook is allowing developers to make money within their canvas pages, through advertising, or transactions that they control.

Amazon is reported to be the first major company to get involved allowing users of the system to publish book reviews on their profile pages. The feature is expected to debut later this week.