Messaging

14. Zimbra

As a messaging and collaboration suite, Zimbra isn't exactly a security solution. However, because it includes built-in anti-virus (provided by ClamAV) and anti-spam capabilities, we felt it was worth inclusion. In addition to the open-source version, Zimbra comes in a multitude of commercially supported flavors that each offer a different feature set. Operating System: Linux, Unix, OS X.

Network Monitoring

15. SNARE

Intersect Alliance offers a number of open-source SNARE (System iNtrusion Analysis and Reporting) agents which provide log analysis for a variety of platforms. If you want commercial support, you can purchase their SNARE server, which is a Linux-based appliance. Operating System: Windows, Linux, Unix, Solaris.

16. Tripwire

Tripwire audit and control software lets you know when changes have been made to your IT configuration. The Enterprise and Server editions are based on the open-source version and offer additional features and commercial support. Operating System: Linux, Unix

17. Nagios

Nagios offers enterprise-class monitoring for systems, applications, or networks. The Nagios Enterprises group offers commercial support and consulting. Operating System: Linux, Unix.

18. Wireshark

"The de facto standard" network protocol analyzer, Wireshark offers deep inspection of hundreds of protocols, live capture for offiline analysis, VOIP analysis, and much more. Support and training are both available through Cace Technologies. Operating System: Windows, Mac, Linux, Unix, BSD, Solaris.

19. ntop network monitoring app. Nmon offers both software and hardware for packet capture and analysis. Operating System: Windows, Linux, Unix.

Passwords and Authentication

20. WiKID

On this site you'll find both the free, open-source community edition of WiKID two-factor authentication software and the proprietary commercial version. In addition to support, the commercial edition adds a few features that aren't available for free. Operating System: OS Independent.

Unified Threat Management (UTM)

21. Endian Firewall

Endian sells a variety of UTM appliances built on the successful, open-source Endian Firewall Community Edition. If you prefer to create your own appliance using an old PC but still want support, Endian will also sell you a supported version of the software. Operating System: Linux.

22. Untangle

Untangle combines 18 separate applications (anti-virus, anti-spam, web filtering, firewall, etc.) into a single package that can be downloaded for free (Open Source Package) or purchased with subscription-based support (Professional Package). Either way, you will need one or more dedicated PCs to run the software, because Untangle does not sell pre-configured appliances. Operating System: Linux.

Virtual Private Network (VPN)

23. OpenVPN

Winner of numerous awards, OpenVPN provides medium and large enterprises with remote access, site-to-site VPNs, Wi-Fi security, and more. Although commercial support isn't available yet, this ap snuck onto the list because the Web site promises that commercial support will be available soon. Operating System: Windows, Linux, Mac OS X, Solaris, BSD

Vulnerability Assessment

24. Nessus

The newest versions of the Nessus network vulnerability scanner are closed-source (though still largely available for free). However, we included Nessus on our list because it's based on the older open-source version, which is still available on the site, and it offers enterprise-grade commercial products for network monitoring. Operating System: Windows, Linux, Mac OS X, Solaris, BSD.

25. Milescan Web Security Auditor

Milescan is the commercial version of Paros. Java-based, this scanner intercepts all http and https data transmitted between server and client to help evaluate the security of Web applications. Operating System: OS Independent.

Web Filtering

26. iSAK