bbPress is free, open source forum software built on top of WordPress. It can be installed as a WordPress plugin into a WordPress powered website. Unlike older forum software, it is not clunky and doesn’t take up a lot of resources. This means it is easier to add a forum to your WordPress site and still keep the simplicity and extensibility of WordPress. It has the ability to create multisite forums, it has customizable templates, and built in support for preventing spam.
bbPress started because miniBB was too bloated for the WordPress support forums. In 2004 the WordPress team decided to code a completely new forum system from the ground up. It was first published on WordPress.org and since then it has been turned into a plugin.
Because it is a plugin, bbPress offers an easy way to add a forum to a WordPress website. It works with most standard compliant WordPress themes. The most popular open source software platforms are usually resource intensive and it is not easy to integrate them into a WordPress website. bbPress solves this problem. It is light weight and can easily blend into a WordPress theme. It was created by the same people who created WordPress so it follows the same principle of keeping things small and lightweight. It is also very extensible and capable of handling custom forums easily. There are also very active support forums with contributors willing to help fix issues and bugs.