g200kg, Japanese developer, made one heck of a simple yet flexible vocoder.
Most vocoders are only made to use as a VST-effect, however there are cases when some sequencers are unable to use a vocoder, simply because of the following problem: ---VST Effect = No MIDI-in. (I've only seen this issue with Sony ACID Pro so far.)
vOcOv comes with a fairly simple carrier module, and a WAV-player system for modulating the signal. The good thing about this is that you can play any note and it'll still play then loop.
vOcOv also introduced a rather excellent feature, from which you have a channel equipped with the VocovCapture.dll as an effect, and with the correct channel routing settings applied, you can control vocoded signals from an external VSTi or WAV stream to do your vocoding through vOcOv. This also works fairly well (despite soundcard latency) with live MIC input and using vOcOv or vOcOv+ext. carrier, to get that whole function those old hardware vocoders have.
A great piece of software, though there can be some improvement on some things (interface, general quality control), but otherwise it's perfect how it is.