Forums are clearly one of the most standard ways of sharing knowledge on the net. With easy-to-use interfaces & strong community features, they are still very functional & popular.

They can be easily integrated into a website by customizing the look & feel or used as a framework which is sometimes a good idea considering the features they offer.

Here are 9 widely-used, open-source & free forum softwares, where most of them are built with PHP, that you may consider using:

phpBB (PHP)

phpBB is one of the oldest & widely used forum softwares around. It is being updated frequently with improvements in speed, security & features.

It comes with a powerful administrator panel where all aspects of the system can be managed & supports almost any database.

The software has a very crowded community which makes it easier to get support.

MyBB (PHP)

This free forum software works with MySQL, PostgreSQL and SQLite.

MyBB has nice features like calendar/events, mass mailing to members, a built-in theme editor & more.

Besides an admin panel, a moderator panel helps managing the system by multiple users.

Simple Machines Forum (SMF) (PHP)

SMF is the PHP successor of the Perl-based forum YABB. It comes with a comprehensive template system, polls, groups, calendars & more.

The software uses MySQL for storing data & has 40+ ready-to-download language files.

Vanilla (PHP)

Vanilla is an open-source, standards-compliant, multi-lingual, theme-able, pluggable discussion forum.

It is built on the Garden, a PHP development framework, which is easily extendible with a powerful plug-in architecture. And, there are already 450+ plugins that are ready-to-use.

Vanilla requires MySQL as the database.

PunBB (PHP)

PunBB is a fast and lightweight forum application which aims to be less graphically intensive compared to other discussion boards.

It supports with MySQL, PostgreSQL & SQLite. The design can be easily updated with the theming support. It is multilanguage & can be extended with the extension support.

FluxBB (PHP)

FluxBB is a fork of PunBB which supports both PHP4 & PHP5 with MySQL, PostgreSQL or SQLite.

It generates “XHTML 1.0 Strict” valid pages & can be easily translated into any language.

bbPress (PHP)

bbPress is a forum software from the creators of Wordpress which is plain, simple & fast.

It can be customized with templates & extended with plugins. And, it integrates perfectly with Wordpress.

Phorum (PHP)

Phorum is also one of the oldest forum softwares. It has support for theming & modules.

The software uses MySQL for storing data

YetAnotherForum.Net (ASP.NET)

YetAnotherForum is a free application that is built with ASP.NET (C#) & uses MSSQL as the database.

It has a feature-rich administrator panel, supports unlimited categories/user groups, templating & more..

Which forum software do you think is the best one, do you have a favorite?