Open source Exchange rival Zarafa has added native support for Blackberry Enterprise Server to a roster of collaboration features that already includes Outlook interoperability, and integration with open source tools such as SugarCRM, OpenERP and Alfresco.

"It connects to BES just as Exchange does, with no need to install anything on the phone," said Brian Joseph, CEO of the software's eponymous development company. 

The Linux-based email and calendaring server also supports Windows Mobile and Symbian smartphones and the iPhone, and has an AJAX-based web client which Joseph claimed has the look and feel of Outlook Web Access.

Zarafa development is currently focused on tight integration with other open source applications via its Z-Merge technology. This uses plug-ins and server-side webservices to link in free alternatives to the likes of Microsoft's Sharepoint, Dynamics and of course Office. 

Now at version 6.2, Zarafa was developed in the Netherlands and is free to distribute under a Gnu Public Licence. Joseph said that the software makes money because while smaller users often choose to implement it themselves, larger ones will usually need some help with implementation and migration. 

"Sure, we lose some 50-user sites, but the growth is in 500-plus user installations - they see it's open and trusted, and go to our partners for support," he said. 

A mid-sized installation might cost €50 to €80 (£45 to £71) per seat in total, making it around half the cost of installing and running Exchange, he added.