Yahoo, an early leader in web-based email, is trying to leapfrog Google with its Zimbra Desktop software, which offers online documents and offline access

The first real fruits of Yahoo's $350m (£175m) acquisition of Zimbra have become apparent, with the release on Thursday of the Yahoo Zimbra Desktop.

The email software, available as a free download for Windows and Mac, works when the user is offline, and offers options for basic online word processing and spreadsheets, task management and file storage.

Zimbra Desktop means that Yahoo has beaten Google in the race to provide email that also works offline. However, Yahoo took a different approach to Google.

Google looks to be adding offline access through the open-source Gears project, a plug-in that augments a web browser's abilities.

Zimbra Desktop, while using the browser-interface technology Ajax, which can give web browsers an elaborate interface, actually runs as a standalone application.

Zimbra Desktop employs Java software to store data locally. It's a substantial download: 38MB for Windows, 34MB for Mac OS X and 44MB for Linux.

Yahoo has formed a new group focusing on cloud computing, in which services available on the internet substitute for local applications. However, until the day when a reliable, fast internet connection is available anywhere, offline access to applications is a significant feature.

Webmail is a compelling facet of cloud computing, letting people reach their email from any number of computers or mobile devices. But, from a user's point of view, Zimbra Desktop's approach — a downloadable application that doesn't run in a browser — is actually more like traditional email client software, such as Microsoft Outlook or Mozilla Thunderbird.

"We've aimed to blur the line between an Ajax web client and a conventional desktop application, and this release is a leap towards reaching that goal," Zimbra's Mike Morse said in a blog posting on Thursday.

Web email comes full circle
Existing Zimbra customers can use the email application through a regular browser, letting them access their email from a machine that doesn't have Zimbra Desktop installed. But the web-client version doesn't offer offline access, said John Robb, Zimbra's vice president of product marketing.

When asked why people should use Zimbra Desktop when standard email-client software has provided offline access to email for well over a decade, Robb said: "The exciting thing is: you're getting the Zimbra features that haven't been available to people without the Zimbra server." Robb specifically mentioned conversations, tagging, small applications called Zimlets, and rich searching features, such as the ability to find all messages from a particular person and with a PDF attached.

Also, Yahoo Mail users can't use the Zimbra browser-based interface yet, so they won't get access to Zimbra features when borrowing friends' computers or using airport kiosks.

Yahoo's Zimbra and Yahoo Mail programmers now are working more closely together, however, and the two projects will, to some extent, be converging.

"You should see a lot of synergy between the Yahoo Mail team and the Zimbra team. This is a first example," Robb said. "You'll see Zimbra technology appearing in many parts of the Yahoo Mail experience, and things from Yahoo Mail will come over to the Zimbra side."

After many months of quiet integration, Zimbra's ascent within Yahoo has been clear. As part of a major reorganisation in June, Zimbra leader Scott Dietzen was appointed to run all of Yahoo's messaging and communication work.

The software can be used to connect to Yahoo Mail and also to other accounts, such as AOL or Gmail, that support remote access via POP (Post Office Protocol) or the newer IMAP (Internet Message Access Protocol).

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