double line with single command?

Say one is drawing a floor plan.  It's very convenient to be able to draw both sides of a wall in one go, setting the gap between the lines to the thickness of the wall.  GenCAD could do it.  Can LC?  Can't find anything.

No, LibreCAD does not have this feature.
There is a tutorial "Draw a house" in our wiki: https://dokuwiki.librecad.org/doku.php/usage:tutorials#intermediate

Wiki looks good.  I'll spend the time when I have the time.