If you're like me then you are finding out about ClearOS for the first time. The open source revolution in the software industry has made it possible to provide ClearOS at no cost, and I think that is a boon for all us IT professionals. 
Among other features, antivirus, antispam, VPN and content filtering are built right into the software -- no need for expensive third party add-ons.  Before making a decision on whether to subscribe to ClearSDN services and updates for ClearCenter, you can take advantage of the free ClearOS download at any time.  One of the most important tasks when deploying server systems is the ongoing monitoring and maintenance.  ClearSDN offers a suite of Gateway and DNS services to make sure your system is up-to-date, secure and running smoothly.  As an open source distribution, you can download ClearOS and receive free security updates for 18 months.  Download, test, play, turn features off, set it up for anything you like - all for free.  There are detailed instructions here and tons of help in the forums