I have no idea what's going on in that thread. :(
basically, a mod that lets you use your brick menu, or some sort of tool, to place down saved duplications of whatever, be it a barricade or a house or something.
if you look on the second page, there's a link to an attempt made by Pie Crust a while ago; the video there helps explain it better.
...i wonder, does RTB even have a duplicator? you might need some catching up to useful/popular mods and their functionality.