I have read about JForum, but I believe it has gone obsolete (not sure).
It is not. It's being developed at
https://sourceforge.net/projects/jforum2/, and there have been constant commits since the last release (which was in February of this year). I think it's the most widely used Java forum software, but that's hard to gauge.
Not Enough videos about it on Youtube too.
Please be kidding about the availability of video tutorials being a criterion for selecting software.
I have also found about Magnolia CMS and Alfresco being out there.
Those are CMS. They probably have a feature that allows you to post comments on a page, but that's far removed from being actual forum software.