ELIZA operated by processing users' responses to scripts, the most famous of which was DOCTOR, a simulation of a Rogerian psychotherapist... It was sometimes so convincing that there are many anecdotes about people becoming very emotionally caught up in dealing with DOCTOR for several minutes until the machine's true lack of understanding became apparent. (Carl Rogers) (Self Improvement?)
Another version of Eliza popular among software engineers is the version that comes with the default release of GNU EMacs, and which can be accessed by typing meta-x-doctor from most modern emacs implementations.
Next level: ALICE/AIML?