I think a few newer German engines and also the older Chrysler 300c v8s do this.
At least the model we imported here in Australia. When you don’t need the power it shuts off 4 cylinders, they keep moving but provide no power. From memory spark/fuel is shut off and as Eric said valves are opened so the pistons are just moving up and down freely, causing little resistance. I have no idea how this works, whether the camshafts for half the engine stop moving, whether it’s the same 4 cylinders every time or it alternates between sides of the engine… it sounds much too complex for a plug and play tuning box to achieve. You’d need to spend serious $$$ to achieve this effect I think.