The Agony Matrix was an energy field-based weapon that Darkseid used against Superman during the invasion of Earth by Apokolips.
History
The weapon utilized, as Darkseid said, direct neural stimulation of every pain receptor in a person, causing unfathomable torture. Likewise, it will have complete effect over any being as long as they have the ability to feel pain, regardless of any level of invulnerability they may have. Superman managed to live through the brutal attack only because of his superhuman attributes and his will. It was almost a certainty that a normal being would have succumbed to the intense pain immediately and died. Darkseid even remarked that Superman impressed him with his resilience as Superman laid on the ground writhing in pain.