@stefano I share with you the ORB Html preprocessor from 1996. This is how I used to build my sites until CMS took over.
https://github.com/OS2World/APP-INTERNET-ORB/blob/master/os2%2FORBMAN.TXT
Yes, it ran on OS/2.
There is also HTMLpp from the same time period - https://imatix-legacy.github.io/htmlpp/
Html preprocessors were a very popular set of early website tools.