Still, the open source model is clearly thriving in the content management space, with these five solutions the standard-bearers out of a list numbering well over 100. Even considering the expected support and customization costs, constructing your CMS on an open source base will give you many benefits of commercial systems -- and still leave you with enough funds to add features that you couldn't normally afford.

Several open source projects attempt to implement Exchange-compatible collaboration servers, but three really stand out: Open-Xchange, Scalix, and Zimbra, each available in commercial and community editions. All three are one-stop Exchange replacements for Linux. Our winner, Scalix, isn't the most feature-rich or innovative of the three (Zimbra is), but it has what most businesses expect from a mail and collaboration platform, along with a solid enterprise pedigree. Originally based on HP OpenMail and recently acquired by Xandros (formerly Corel Linux), Scalix sports a Web-based administration interface, strong Outlook and Novell Evolution integration, POP and IMAP standard servers, and a rich, Ajax mail and calendar client.

As is the case with Open-Xchange and Zimbra, Xandros open sources Scalix's foundation while setting aside the most lucrative bits as closed source. The open source Scalix does not implement the full Outlook client feature set. However, the downloadable binary Community Edition includes licenses for 25 "premium" users, and those users can effectively use Scalix with Outlook as though they're talking to Exchange.