Audio Damage is a small software developer that is quickly gaining visibility in the plug-in world. Some of their plug-ins are ranging from idiosyncratic to weird, others are emulations of existing hardware. For the intersection, check out their Ratshack reverb. The image of the company is partly formed by two things: the excellent look of their GUIs and the 3D mock-ups, and the fact that they don't have demo versions of the software. As they argue in the forums, demos are a support headache, and don't appreciably add to sales.
One plug that doesn't seem to have an immediate hardware counterpart is Discord. In version two, this is a combination of two pitchshift/delay lines, with all elements modulatable by LFO, and with crossfeeding between the two lines.
With these elements, all sorts of effects can be attained. Small static shifts can thicken a sound, shifts of several semitones add artificial harmonies, but I've been having most fun with putting a delay on the shifts. For instance a whole beat delay (unfortunately the delays can not be tempo synced) combined with a whole tone shift gives an interesting second voice to modal music. Also the cross feeding between the two shifters can give interesting effects: imagine two different shifts feeding into each other, resulting in an ever rising sound.
In sum, I am not sure where this effect would fit in with acoustic and more traditional music, but it is wonderful to muck up electronic sounds. Instant weirdification.
Like all Audio Damage effects, the price is very reasonable, there are presets to get you going, the effect is pretty easy to understand but there is a manual, and email support has been quick and effective.