pst-osci is a PSTricks package enables you to produce
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.