Eliza is a famous old program that attempts to converse with the user in English sentences. It is, in reality, an almost total sham - but a very interesting one. I'm always suprised at how easily it sucks people into believing that it must have some understanding, or at the very least must be quite complicated. See for yourself.
Includes C source code (generic or older Borland C).
ELIZA.ZIP 18,024 bytes