Kunena is the leading Joomla forum component. Downloaded more than 8M times in 11 years, Kunena is the only forum/discussion solution for Joomla that is community driven - true open source - public self-help forums, GitHub and documentation Wiki.
The most recent stable release, recommended for production websites running J! 4.3/4.4/5.0, is Kunena 6.2.1
For websites running J! 3.10 there is Kunen...