For Freud, agency (german Instanz , French instance ) refers to one or other of the various substructures of the psychical apparatus. Examples would be the agency of censorship in the first topography, the agency of ego or super-ego in the second topography.
"Agency may be coextensive with life. Life certainly burgeons nowhere without agency. We act on our own behalf. In the Kantian form: What must something be such that it can act on its own behalf?" (Stuart Kauffman, Investigations, p.49) For Kauffman, autonomous agents, defined as autocatalytic systems that can reproduce and carry out work cycles, define life. He emphasizes that "all free-living systems we know -- single-cell bacteria, single-cell eukaryotic cells, and multicelled organisms -- fulfill his definition of an autonomous agent.
For Marvin Minsky, human understanding functions by running multiple representations in parallel through agencies he calls the "society of mind." Thus, "If you understand something in only one way, you do not really understand it at all. If something goes wrong, you will be stuck with a thought that just sits in your mind with nowhere to go. The secret of what anything means to us depends on how we have connected it to all the other things we know. If you have several different representations, when one approach fails you can try another. Well-connected representations let you turn ideas around in your mind, to envision things from many different perspectives, until you find one that works for you." (from Scientific American, October 1994) (cf metaphor)