FUDforum (Fast Uncompromising Discussion Forum) is a free and open source web discussion forum released under the GPL (version 2) license that is written in PHP and can be used on virtually any operating system. $5/month
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FUDforum (Fast Uncompromising Discussion Forum) is a free and open source web discussion forum. FUDforum combines an extensive feature set while maintaining the ability to generate forum web pages extremely fast. The forum includes i18n and templating support allowing for a complete customization of its output as well as a very capable group based permission system. FUDforum can also act as a Mailing List Manager, USENET newsreader and even an XML Feed Aggregator. This will allow you to build an instant community and consolidate all your messages into a single system.
FUD Forum stands for, ‘Fast Uncompromising Discussion Forum’ and has been available for well over a decade now and continues to get updates and improvements. The platform is written in PHP and is coded quite efficiently to help keep it responsive and stable. It is generally recommended for very large forums with hundreds of thousands of users and millions of posts. Of course, it will also work fine with smaller communities.
The system is completely free to use and open source. It is one of only a few free forums platforms that is recommended for large communities. The developers have done a great job at balancing features with performance, and also weaving in excellent security to the entire system. This really is one of the better forums platforms out there today, and one that anyone looking to have forums on their site should consider.