Redstone Columns allow Zero Delay redstone signals to be sent upwards/downwards. They only pass a redstone signal to another Redstone Column or a Redstone Column Circuit. A Redstone Column Circuit is required for the input redstone signal. When Right Clicked while holding no items/blocks the Redstone Column changes between the two modes. By default it won't connect to blocks at its sides and won't pass on the redstone signal it gets to them, but when switched to its alternate mode it will send a redstone signal to all 4 of its sides.

The Alternative mode allows you to make things like a Zero Delay Piston door where all the Pistons activate at the same time, no matter their height.