using two multiplexer ICs and some TTL logic, you can view eight analog or digital (or some of both) signals on the oscilloscope
http://www.edn.com/archives/1997/011697/02di_03.htm
uses a matrix of 100 LEDs for a display
http://www.geocities.com/SiliconValley/Lakes/7156/articl3.htm
put many traces on a single input oscilloscope.
http://www.intio.or.jp/jf10zl/mulv.htm
http://www.multimeterwarehouse.com/dictionary.htm
Miniature TV converted to simple oscilloscope - Notes on converting that old compact tv set or computer monitor into an oscilloscope. Proves very useful in line quality monitoring and other low frequency applications.
http://www.dansworkshop.com/Homebuilt%20oscilloscope.shtml
Oscilloscope Block Diagram and Schematics by N4BCU
http://members.tripod.com/michaelgellis/scope.html
http://www.ee.washington.edu/conselec/CE/sp95reports/guterman/final/scope1.htm#hard
Schematic for a lean, mean, four channel digital oscilloscope based on the 28-pin 16C55 HS PIC, a 64K x 4 DRAM, and a resistor network configured as a voltage dividing DAC. When the record button is pressed, the PIC captures and stores 64K samples from th
http://home.iprimus.com.au/vk3jaj/logic4ch/index.html