The purpose of this project is to design an interactive animated digital filter design tool that can be used both in engineering design and education.
You can read the summary of the project . But some of the information is dated.
Here is a current sample screen shot of the program. The applet implementation of the program is here, but it only works for IIR filter with Butterworth approximation in Bilinear transform, but you can design highpass, lowpass, bandpass, bandstop filters. More functions are coming. Please email me your comments. In the mean time, you can read the decumentation generated from javadoc in here.