[pjtr]

The one I remember was "voxel.pas by Steven H Don". A Delphi port survived here: http://tothpaul.free.fr/sources.php?dprgrp.voxel

Searching for "voxel" in https://github.com/nickelsworth/swag/ also finds some very similar tiny Turbo Pascal programs.

[pjtr]

A short article titled "Voxel Landscapes 2D and 3D By Scout/C-Lous" described most of the tricks, but I can't find the text anywhere. A similar article by the same author on another topic I found here https://github.com/ggnkua/Atari_ST_Sources/blob/master/Docs/...