This mod is for Luanti/minetest only.
I made it with a little help from AI (read made by AI completely), and its purpose is to help in building objects/converting materal. The commands are simple and as follows;
/pos1: Sets position one, one corner of the area.
/pos2: Sets position two, the other corner of the area.
/setnode: Takes object in hand and makes it the replacment for anything replaced.
/fill: Basically a replace command; it finds all except air and water blocks in the area selected and sets them to the /setnode node, whatever that might be (note, this will cause the server to crash if it's not an item you can place normally.)
/airfill: Adds setnode to all blocks between pos1 and pos2.
/delete: Converts all blocks between pos1 and pos2 to air blocks.
Screenshots: The first is before doing anything. Second is setting pos1, third is pos2, fourth is setnode, fifth is fill and sixth is airfill. Have fun, and I would like feedback!