Free & Open Source PHP Forums
Filters Web Servers: All, Databases: All.
PHP Language is the most common and most used programming language on Internet. It is available on almost all platforms, is easy to learn, easy to understand, and customizing or modifying an existing project based on this technology is within the realms of possibility.
However, due to this relative simplicity, non professional (Note: ≠ from free or open source) forum software could easily be a nest of security issues.