The idea is to provide the familiar Office functionality and user interface in web applications that can be used almost anywhere that a web connection is available.
Michael Schultz, director of marketing for Microsoft Office Services at Microsoft, said "these are the online extensions of the well-known desktop applications that customers can use where they want, when they want. The application interfaces will look instantly familiar, and documents maintain their fidelity, whether working in the cloud or in desktop applications."
He added "we’re making the Office Web Apps accessible across PCs and Macs, and available using Internet Explorer, Firefox or Safari."
The technical preview program gives participants access to early versions of Word Web App, Excel Web App and PowerPoint Web App. A OneNote Web App is also under development.
Following the lead of Google and other developers, Office Web Applications will allow people to collaborate on documents.
More features will be added to the apps before they are made public, and closer integration with Office 2010 is planned. One example will be the ability to embed documents in blog posts and other web pages.
The invitation-only technical preview will be followed by a public beta and the release of the service in the first half of 2010.
As with other web applications, Microsoft's stated strategy with Office Web Apps is to make frequent updates based on user feedback, rather than the traditional 'big bang' update cycle.
Office Web Apps will be offered three ways: via Windows Live, as part of Office 2010 volume licensing (using on-premises SharePoint Server), and via Microsoft Online Services.