Thirteen years after Netscape flirted with the idea of turning its successful web browser into a fully fledged operating system, Google has offered users the chance to ditch their Windows licences.

Chrome OS, initially available for netbooks, will eventually run on desktop computers, offering a realistic and low-cost alternative to Microsoft Windows.

The system is likely to appeal to home users, partly because there will be no installed applications to keep up to date and partly because of Google claims that it will not be vulnerable to viruses or other malicious software. It should also start up very quickly, and will integrate closely with Google’s online services, including Gmail and Calendar.

Chrome OS may make it easier for users to use online applications instead of having to buy licences for Office and other Microsoft tools. It will not look like other operating systems, where the web browser is just one application among many. Google has positioned it as a browser support system, rather than a traditional computer operating system.

The system will concern Microsoft, which hopes that its release of Windows 7 in October will help customers to forget the problems with the previous model, Vista, and that its plan of having powerful desktop computers running local applications that integrate well with online services will slow the move to cloud computing.

Bill Thompson is a technology writer and broadcaster

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