Zimbra will release a second beta test of its messaging and calendaring software and introduce <A HREF="http://news.zdnet.com/2100-9593_22-5951725.html?tag=zdnn.alert">a version targeted specifically to businesses.</A> Using an open-source business model and a modern development technique known as Ajax, the start-up is looking to unseat entrenched messaging suppliers IBM and Microsoft. The company, which launched its first beta in August, makes its Web-based messaging product available for free with an open-source license. It intends to make money by charging corporate customers a license fee for a more functional "Network" version and a yearly support fee based on the number of mailboxes used.