‘Rectangular selection tool’ is an idea to allow simultaneous selection of several things at the same time. The player would use it in 2D screen space to select things (within range) that are ‘behind’ the 2D screen space he’s seeing.
The player would activate the selection mode/tool and click the ‘corner’ of an area he wants to select things in, then clicks the ‘opposite’ corner of area to select, and then everything that is inside of the rectangle gets ‘selected’. This would potentially be useful for selecting structures for mass-marking or mass-deconstruction by a designated builder (instead of running up/next to each thing to mark/decon it).