Unison - replace Exchange and Outlook with a single Linux based Unified Communications Server
According to a recent PC World article, the software company Unison has just launched a unified communications suite, akin to Exchange and Outlook, which features e-mail, messaging and VoIP. The software, also called Unison, integrates IP telephony (VoIP), e-mail and instant messaging with a diary, address book and presence capability. All of this will be rolled into a single Linux Server. Currently, you can get it as a free public beta.
This is a step up from the traditional Microsoft schema like Microsoft Office Communications Server which often require multiple servers to accomplish the same task. The time to production is also drastically cut down to less than a day for an experienced Linux administrator. There is a Unison client program for Windows which replaces Outlook.
Current configuration supports between 20 and 300 seats, but there are future plans to support clustering for scalability. Open-source technologies are incorporated into the solution stack like Thunderbird for e-mail and Jabber for Instant Messaging. Some custom code was also written by the Unison developers. The beta is said to be stable and ready for any organization to deploy and test. You can get more information at Unison.com