Basically, it's just the Traveller's Belt from Tinkers', but it's for 1.10.2. It switches between n hotbars, instead of 2, though. You can add additional hotbars to your fanny pack with nether stars.
Craft and equip the Fanny Pack to your belt slot, and you can now press the hotkey (backslash by default) to swap your 9 hotbar slots with another hotbar. You can keep your blocks on one, tools on another, and bags of holding on yet a third hotbar!