SmallWall history actually begins with m0n0wall. Manuel Kasper, m0n0wall's author, says:
Ever since I started playing with packet filters on embedded PCs, I wanted to have a nice web-based GUI to control all aspects of my firewall without having to type a single shell command. There are numerous efforts to create nice firewall packages with web interfaces on the Internet (most of them Linux based), but none met all my requirements (free, fast, simple, clean and with all the features I need). So, I eventually started writing my own web GUI. But soon I figured that I didn't want to create another incarnation of webmin ? I wanted to create a complete, new embedded firewall software package. It all evolved to the point where one could plug in the box, set the LAN IP address via the serial console, log into the web interface and set it up. Then I decided that I didn't like the usual bootup system configuration with shell scripts (I already had to write a C program to generate the filter rules since that's almost impossible in a shell script), and since my web interface was based on PHP, it didn't take me long to figure out that I might use PHP for the system configuration as well. That way, the configuration data would no longer have to be stored in text files that can be parsed in a shell script ? It could now be stored in an XML file. So I completely rewrote the whole system again, not changing much in the look-and-feel, but quite a lot "under the hood".
The first public beta release of m0n0wall was on February 15, 2003. Version 1.0 was released exactly one year later, on February 15, 2004. Between those two were an additional 26 public beta releases, an average of one release every two weeks. Version 1.1 was released in August 2004, with 1.11 released with a security update for m0n0wall's dynamic DNS component ez-ipupdate on November 11, 2004. This was followed by the 1.2x series, and the 1.3x series, and then the 1.8.x series, where the versions changed to map to FreeeBSD versioning. On February 15, 2015, 12 years after starting, Manuel Kasper announced the closing of the m0n0wall project.
Some people disagreed... After significant activity on the mailing lists and in the forums (before they closed) Lee Sharp began the SmallWall project. It is not a radical departure from m0n0wall, but a continuation of a small and purpose built firewall that many people feel there is still a need for today.