pst-osci is a PSTricks package written by Manuel Luque and Christophe Jorssen to draw easily oscilloscope screen shots. Three channels can be used to represent the most common signals (damped or not): namely sinusoidal, rectangular, triangular, dog's tooth (left and right oriented). The third channel allows you to add, to subtract or to multiply the two other signals. Lissajous diagrams (XY-mode) can also be obtained.
Current version is 2.7, from November 17, 1999.
It is available on CTAN/pstricks/contrib/pst-osci (and require also the file pst-key.tex available on CTAN/pstricks/contrib/misc).