I've just been doing some exploring on the other forum site which I used as a model for several of the suggestions I've been nagging you about (e.g. Preview), and it appears they use software called simple machines. I then found this link. Is it of any interest to you, or are you already aware of it (in which case just tell me to go away ;-)
That link goes to a web hosting service that can handle SMF hosting (as, indeed, can almost every other host in the world anyway). The open source software link itself is actually here:
https://simplemachines.org/