At least version 5.1
An SQL database server / system. Currently, SQLite (at least version 3) and MySQL (at least version 4) are supported. Support for others can easily be added, provided they can be accessed via PHP's PDO.
The main development system runs Debian GNU/Linux, Apache 2 and SQLite. In theory, Spam Board should also run on Microsoft Windows, but that hasn't been tested (feel free to edit this if you do).