Fourier Series is a simple, totally free program that requires no installation and is run in MSDOS.
Fourier Series comes equipped with a collection of mathematical functions to graphically represent the Fourier series. You can present that series as a triangular wave, a square wave, a saw tooth wave, expansion of the sine and cosine, an interrupted square wave, etc. Without doubt it is a practical and very visual way to study the graphic behaviour of the Fourier Series.
The whole Fourier Series interface is controlled via the keyboard or via a combination of keys.