Stempel is a free vocoder effect for Windows.
Here’s a preview of what you can do with it:
If you’re on Windows, give it a try and leave a comment with your thoughts!
Stempel operates in the frequency domain to print the magnitude of an input into the other, giving the vocoder effect, but with a smoother sound and a higher analysis definition than with classic time domain vocoders effects. Additonally, the effect features a two states morph-able spectral equalizer, a linear frequency shifter on each input channel , and two additional time domain effects ( a saturator and a chorus ).
Stempel is licenced for free. The distributed zip archive includes a detailed pdf manual and some fxp presets.