Stacked x2/x3 Hotbar Question

I've seen, on multiple occasions, people using a double stacked/triple stacked hotbar.

I'm wondering, what extension/mod is this?.

I'm aware that there are plenty of alt/hotbars, using shift/ctrl/alt ect. but what Id really like to get, is a doubled or triple stacked variant (containing the ctrl and or ctrl/shift bars up front and center) -- anyone know of the relevant mod/extension.. a stable and reliable one?

Even better would be a 24 slot variant, single row - with icons/tooltips. save some space.

As far as I know, there is no double/triple stacked hot-bar extension. You can select different hot key bars using combination of modifier keys: Shift/Control/Alt.

Regards,
JPG