Some operators using single crew certified aircraft, operate a multi-crew environment by way of a Pilots assistant. These assistants, usually PPL holders, assist the commanders management of the aircraft by operating the radio, keeping the plog up to date, and locating the correct Jeppesens !!!
They are also useful in liaising with the passengers. (serving the coffee).
King Air B200's are the only ones I know of, altough I'm sure someone will be along shortly to add other types!