Zimbra offers both options for users, too, as well as e-mail, contact management and calendaring features. But its new Zimbra Documents feature makes use of AJAX Linking and Embedding (ALE) technology, so users can nest a number of documents within a single e-mail message and then invite their colleagues to edit the information.

"People really like to live in the tools they're comfortable with," said Rob Enderle, an analyst at Enderle Group. Zimbra hopes to succeed where rival IBM failed in getting users to "live and breathe" within its collaboration software, he said.

Three-year-old Zimbra officially launched its first software last October. ZCS 4.0 also features Zimbra Mobile, which provides native over-the-air synchronization between the groupware and a range of mobile devices, including smart phones from Motorola Inc., Nokia Corp. and Palm Inc. Zimbra has yet to offer native support for Research In Motion Ltd.'s popular BlackBerry device, currently relying on partners like Notify Technology Corp. for that capability. But it hopes to make that support available in the future, said Zimbra President and Chief Technology Officer Scott Dietzen.

Zimbra has around 200 paying customers, ranging from small to midsize businesses with 50 seats each to an unnamed Internet service provider that has millions of users, according to Dietzen. Customers the start-up does publicly identify include Firefox Web browser creator Mozilla Corp., Brazilian Internet service provider Orolix and tax services provider H&R Block Inc.

Osterman warned that users who need features beyond the groupware ones offered by Scalix, Zimbra or a third open-source vendor, Open-Xchange Inc., may find themselves saving less money than they expect. "If you need integration with Office or Live Communications Server, or a document repository, or have a very distributed organization, you could lose the cost advantages you were seeking," he said.