I've used the YaBB forum and found it reasonable to manage. Stores messages as files. It's quite mature, there are numerous extra features (mods) but the main developer recently died.
Comment on Re: What is your favourite Perl-based forum software?
Thanks for the reminder about YaBB. I did look at it maybe 15 years ago along with eBlah but decided to go with the latter for reasons which now escape me. That turned out not to be a good choice as eBlah development ceased shortly afterwards. Alas it seems that the same is now happening with YaBB with most (all?) of the dev team gone and the last commit being nearly 2 years ago. A real shame.