NuTone home intercom system – you can talk to or pipe music (with separate AM and FM dials!) to people elsewhere in the house. This was at an estate sale, but in college I lived in an old house that had one of these.
Above the unit: a diagram of the house and corresponding switch numbers, disguised as 1970s art. Really, take a closer look it.
Below the unit: Beige switchplate painted brown(!) to match the wood panelling that has been rubbed clean from years of use.