Example Open Source Solutions
Zimbra vs. Microsoft Exchange
Microsoft Exchange e-mail server software has a $699 base cost, with a $67 per-user cost. Additionally, there are some other costs for additional features such as anti-spam, anti-virus and others. Additionally, you must have Microsoft Outlook to connect to Exchange and use all its features, often requiring the additional expenditure for Microsoft Office. This would cost a typical 25-person company in the neighborhood of 2400$ for the basic feature set.
Enter Zimbra, an open-source, fully functional Groupware suite with advanced features with nothing more than a per-user cost of 35$ per user annually and it even costs less the more you buy! (28$/user for 50 or more users). This comes with anti-spam and anti-virus features right out of the box. That means that for a 25-employee company, that's an immediate savings of 1400$ on e-mail functionality alone.
Along with the savings in money comes the knowledge that you won't be held captive by your technology, as Zimbra uses open standards for storing and accessing its data. This means that you're not at the mercy of some company if you choose to change your mind. It's your data, take it with you!
