Zimbra Desktop is a new web service that lets users check and edit emails even when they're not connected to the internet.

Taking on Microsoft and its forthcoming range of web-based applications, Zimbra Desktop offers a webmail account, file sharing, calendar functions and synchronisation with mobile phones.

The latest application added to Zimbra Desktop is an open source email service that lets users read and reply to email messages even when they're not online. This should be good news to mobile workers in transit without an internet connection.

Zimbra Desktop - still at alpha testing stage - uses a local database on a computer's hard disk. Every time a user connects to the internet, the database syncs with the Zimbra webmail server. When the user is not online, the email messages can still be accessed via the local database stored on the hard disk. In other words it does what desktop email clients like Outlook and Apple's Mail have been doing for years, albeit with a webmail component.

A beta version of the web application will be released this summer, Zimbra said. The beta version will add POP and IMAP support to the webmail service.

Zimbra is a wholly web-based service, and works with Windows, Mac, and Linux operating systems.