AJAX-based online tools (define) typically offer nearly all the dynamics of desktop applications save for one: offline viewing.

When you're not connected to the Internet, you're not connected to your data, which is what AJAX helps to streamline. But that's about to change, thanks in part to an effort from open source collaboration vendor Zimbra.

Starting tomorrow, Zimbra will be making its offline utility publicly available as an alpha release. The company calls it the Zimbra Desktop. It's available on Windows, Linux and Mac platforms.

The alpha release is still missing a major functionality, namely calendaring. Zimbra Co-Founder and CEO Satish Dharmaraj told internetnews.com that the next release of Zimbra Desktop, expected in early summer, will include support for offline calendaring in the same way that Outlook users can integrate with offline calendars today.

Though offline AJAX capabilities have not been implemented before, Zimbra users will recognize the method it uses to synchronize with its online counterparts. The company has been telegraphing its intentions for some time.

For example, Scott Dietzen, president and CTO of Zimbra, explained to internetnews.com in November that Zimbra was developing an offline utility that would act as a Zimbra agent to recreate all the data needed for the same browser experience, connected or not.

Dharmaraj explained that Zimbra will be using the XML over HTTP (XHR) approach to syncing local with remote data. Zimbra has always used XHR (define) to get synchronization with the Outlook MAPI (define) protocol for Zimbra to Outlook synchronization.

Zimbra offline works by way of a small http server installed on the local user's machine, which uses the Apache Derby database to maintain the Zimbra information store. On top of that, Zimbra implements the Apache Lucene search application to provide full search capabilities to the offline client. A shortcut is placed on the use desktop, which points to the local service enabling the offline functionality.

Though Zimbra desktop is installing a Web server on the user's desktop, it is not expected to trigger any kind of access control alerts. "Access controls are not an issue because the service doesn't run on any restricted ports," Dharmaraj said. "The Zimbra desktop is running on port 7000 and it's an open user port used to run at the user level."

Zimbra's offline AJAX effort is not the only attempt in the industry at providing offline AJAX capabilities. The open source Dojo Framework is also working on an offline effort.

"If we had started Zimbra today we'd probably use the Dojo framework, but there was no Dojo when we started," Dharmaraj said. "Our app is complex and the Dojo offline experience allows offline access if you want to store a few attributes from a web app and then access it locally.

"What we have are documents, calendars searching tools, tags and a database for conversation, so it's a much more complex offline store capability versus an attribute store that dojo offers," Dharmaraj added. "Dojo offline is useful for lots of apps but for complex apps like Zimbra we had to do it ourselves."