As Metin Seven mentioned in his MagicaCSG Blender thread.

A free demo of the little SDF-Modeler "MagicaCSG" is now
available (PC only and for non-commercial use only). The range
of Features is somewhat limited compared to the Patreon
version but still workable.

This Modeler is made by "Epthracy" the same guy who
made "MagicaVoxel"

You can download it here:
https://ephtracy.github.io/index.html?page=magicacsg