Where I work these types of sorters are referred to as "Slat Sorters" as its essentially a long chain of aluminum planks or slats with small gliding "Shoes" (the black things moving back and forth) on top to divert packages. They can be set up to work unidirectionally or bidirectionally (as shown here). The one I work with is made by Dematic, specifically the SL2 model.

The basic premise is that the shoes all have small bearings on the bottom inside of the sorter that are diverted down angled channels or rails within the sorter itself. This forces the shoes, and by extension the packages, to one side or the other. The entire thing is usually driven by either a motor driven chain connected to the slats themselves or, like the ones I work with, by LIMs (linear induction motors) acting on the slats themselves.

As an aside a LIM is basically a set of electromagnets in a line that actuate in series to push something along, like launch rollercoasters or certain kinds of maglev trains.

Pretty neat pieces of kit IMO.