If you are looking for a firewall solution, consider PFSense. I have used various firewalls over the years, including homemade solutions, Sonicwall and other paid solutions, and now PFSense, and I find PFSense to be the best of the bunch.
Teaching Data Structures
While teaching CIS 263 - Data Structures, I went spelunking around the web to see if there were any decent pre-made visualizations (or animations) that I could use to illustrate various data structures. As usual I spent a few hours hitting dead-ends until I figured out exactly what to ask Google for. Ultimately I found a site maintained by the Computer Science Department of the University of San Francisco. This site provides animations for a large variety of data structures (listed here, provides controls for working with the data structures, and even allows stepping through and back through data structure operations.
If you are teaching or learning data structures this site is an indispensable tool. Kudos to David Galles, who maintains this site.
I am porting my old site to a new framework, so forgive the mess. Give me a semester to work out the bugs.