Discourse is an open source discussion platform built for the next decade of the Internet. A modern forum, everything's been redesigned to be easy.
uCoz is a free website-builder that includes hosting and a website management system. uCoz works according to the principles of Web 2.0 and allows creating of the most complicated projects with extraordinary simplicity and speed.Warning
Blocked by Google chrome, many DNS plugins and is known to be dangerous to many experts.
Since its creation in 2000, phpBB™ has become the most widely used Open Source forum solution. Like its predecessors, phpBB™ 3.2 “Rhea” has an easy to use administration panel and a user friendly installation process, which allows you to have a forum set up in minutes.
bbPress is forum software with a twist from the creators of WordPress. Its focused on web standards, ease of use, ease of integration, and speed. bbPress will try to keep things as small and light as possible while still allowing great add-on feature possibilities.