bbPress.org

Yes, put it in it’s own folder, inside the WordPress folder. So you might have something like this:

/var/www/public/website/wordpress

/var/www/public/website/wordpress/bbpress/

The 404 error might be because you are trying to use permalinks, either “slugs” or true, and they’re not set up on your server. I would change them to false for now and see if you can get the links to work. If that works, then you know that was the problem and you just need to set up permalinks.

https://bbpress.org/documentation/faq/#pretty-permalinks

phpBB3 conversion:

https://bbpress.org/forums/topic/phpbb3-converstion

I don’t think so, not easily, not yet. I think there was a script to export phpBB2 to bbPress:

https://bbpress.org/forums/topic/a-phpbb-to-bbpress-database-converter