A three-prong to two-prong adapter is also known as "AC ground lifter" or "cheater plug". What is a single socket to ground-only plug adapter for electrical outlets called? It's a single socket adapted into a single metal ground prong, accompanied by insulated prongs for hot and neutral only to keep it firmly attached to the outlet. I've seen an example of one here called "Ground Plug Adaptor", whose socket accepts a banana plug, but I don't know whether the name is vendor-specific. That name doesn't indicate what goes into the adapter's socket. Googling "Ground Plug Adaptor" gives some cheater plug results.
I want this for purposes of grounding shielded Ethernet (possibly powered, e.g. PoE, PoE+, or passive PoE) cables' drain wire. In an industrial setting, these are grounded automatically when attaching shielded Ethernet keystones to patch panels, whose equipment rack has a grounding lug. I'm in a house, and my Ethernet keystones are mounted to a plastic multi-slot wall plate. I want to use the empty slot for a single socket keystone (maybe a banana jack) that bridges all the Ethernet cables' drain wires together, then connect that keystone to this ground plug adapter, and connect the latter to a grounded electrical outlet.
I also want this for purposes of grounding a person via anti-static wrist strap when working on electronics to prevent electrostatic discharge from damaging the components.
I'm in the United States.