As if Open Office, Adobe's Buzzword, Google's Docs and Lotus Symphony weren't enough, Microsoft Office has yet another rival willing its downfall from the lofty Microsoft perch.

And, what's more, it's kind of an enemy within. One of the co-founders of Hotmail is behind Live Documents, a new business which hopes to tap into Microsoft's Office market - which The Times estimates represents a third of Microsoft's total revenue. Live Documents is a full-featured suite of online Office productivity applications offering functionality equivalent to Word, Excel and PowerPoint.

Sabeer Bhatia's software is, like many of the rivals, available free online. Unlike Microsoft, Adobe is one of the few established software providers to acknowledge there will be a fundamental change in the way we attain software during the coming years.

"We are just a few years away from the end of the shrink-wrapped software business. By 2010, people will not be buying software," Mr Bhatia told the newspaper. "This is a significant challenge to a proportion of Microsoft's revenues." Although the software is free for individuals, companies pay for the system, which can be hosted remotely or on their internal server - rather like Google Apps.

Live Documents will be available shortly and comes complete with 100MB free online storage for individuals.

Bhatia launched Hotmail before eventually selling to Microsoft in a £400 million deal. I believe that Live Documents does for documents what Hotmail did for email," said Bhatia.