Forum scripts - xmbforum2
XMB forum has been an open source project and in use for many years: https://www.xmbforum2.com/ and many other forums were based on XMB, mybb being one.
Bugs: https://bugs.xmbforum2.com/my_view_page.php
Doco: https://docs.xmbforum2.com/index.php?title=Main_Page
Community forum: https://forums.xmbforum2.com/
XMB is not overly mobile friendly and needs some friendly loving from devs, probably CSS expertise