This program is a software channel vocoder, which imposes vocal effects on a waveform. It can be used to make your voice sound "robot-like", to create a singing synthesizer, to disguise your voice, and many other fun things.
ZVocoder is a small application that will take two sound files and combine them into a new sound file through a vocoding algorithm. A vocoder is typically used to combine a speech sound with a frequency-rich musical sequence to generate a robotic-sounding singing voice. It has been used widely by many musicians.