There are many PHP scripts ready to use for a PHP forum or board site, but only a few are very popular. It is very important that a CMS script to be updated often with security fixes because the hackers are discovering periodically different bugs that can be exploited, the PHP, Linux and in general the entire LAMP stack is updated, some functions are removed and others are deprecated and is important that a script to be updated at least a few times in an year.
Most of free forum platforms are available for download and you have to host them on your server. In our comparison we have included only the best and most popular forum software written in PHP, the most used programming language for websites. We did not included bbPress forum platform because is not independent and you must have Wordpress installed.
Updates & Security
Look on the developer's website at the download or changelog page(s) to see on which date was released the latest version. Forums are often the target of spam robots and you would like to have a platform that is constantly updated.
Features & Demo
Most of the free platforms offers a demo and you can see the featured of the admin control panel. Also, take a look at their support forum and see what plugins are available, if they are rated and updated.
The free forum platforms offer all essential features like the paid ones, but in general their design is not better and the updates are released slower.
phpBB, MyBB and SMF are very good choices. If you want to compare free and paid forum platforms then take a look at this page.