[selcuka]

I also remember that the first web based forums used a Perl script that actually created new HTML files on the web server when someone posted a new topic, and modified the existing one when someone posted a reply.

A bit similar to static web site generators today, only with endless security vulnerabilities.

[krapp]

You might be referring to the venerable wwwboard from Matt's Script Archive, which amazingly still exists: https://www.scriptarchive.com/wwwboard.html

[selcuka]

It's been almost 30 years, so my memory is hazy, but that really looks like it.

It still exists but last updated in 2000. It might be fun to make a Docker container with the right dependencies (if that's still possible) to run it.

[dcrazy]

I believe UBB (Ultimate Bulletin Board) worked this way too.