I remember a lot of ads in Byte magazine in the early 1980s showing Apples, TRS-80s and CPM machines with a biorhythm chart displayed on the screen.
Also, for some reason recipe storage was also considered a killer app, as if someone would use a $3000 computer in the kitchen for displaying recipes, as opposed to a $10 cookbook or a $2 box of 3x5 cards.
EDIT: beaten by dropzone.