Oscilloscope clock
nycresistor.com
nycresistor.com
I still remember mapping out all 36 letters/numbers as XY coordinates.
You can actually output decent vector graphics signals from a sound card if you jump through some hoops to be able to output a reasonable DC signal.
Somewhere I've got a copy of the Scelbi-Byte Primer which has an article from 1979 called "Beer Budget Graphics" where an R2R ladder is used to create a point display on an oscilloscope. Its tougher when you're using a 4Mhz processor :-)
EDIT: Update apparently its from the November '76 issue of BYTE.