Any chemical, physical or mechanical substance or material used to enhance or facilitate a desired effect, such as anemulsifying agent, or a wetting agent.
In multimedia, an agent is any animated figure that explains how to operate a particular software application.
In computing, an agent is also any program designed to perform a repetitive task, much like a macro. Also known, in this sense, as a softbot, a contraction of software robot.
An agent is also a person responsible for procuring work for clients, or for procuring talent to work on specific (usually freelance) projects. Examples are literary agents, employment agents, etc.