As Microsoft moves to offer software-as-a-service with Windows Live, online companies are moving to challenge Microsoft on the desktop. In a decision that would have been seen as foolish a few years ago, file sharing and social networking company TransMedia plans to release desktop productivity apps (in conjunction with online ones) as lightweight Microsoft Office alternatives. Google, meanwhile, through its deal with Intuit, is colonizing desktop apps as it has done with browsers and search toolbars. Microsoft used to have a home field advantage on the desktop, thanks to Windows. Lately, operating system ownership is looking a lot less valuable.