These are NetGear XE104 switches. They are very clever and communicate with each other over the 110V wiring.
Nowadays there is not much call for these because wireless is so good, but the odd person will still find these useful for getting a printer connected in the corner of the house or people with houses with brick walls that are too hard to get wireless or wire through the walls.
Because of these niche use cases these are still sold on ebay and amazon.
They are $23 on amazon (free shipping).
They are $13 on ebay (no free shipping).
I will sell mine for $60 ($15 each), but must take all four.
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