ABS plastic boxes can be stacked and latched together allowing several tools to be moved at once.
The top handle recesses into the lid so another box can be stacked on top of it; the two boxes are joined at the rear by mating slots and tabs and at the front by a rotating T-Loc mechanism.
Older Systainers and current Tanos boxes use clip-like latches to hold lids closed and gang boxes together.
These jumbo-size boxes have twice the footprint of standard models, but they're still modular. You can gang them to each other or put a pair of standard-size Systainers on top.