Oli Larkin has released version 2.0 of the Endless Series, which includes the addition of Endless Shifter and Mac OS X VST, AU and RTAS support (via the Pluggo runtime).
The Endless Series are four effect plugins based on an auditory illusion known as "Circular Pitch" or more commonly the "Shepard Tone/Scale" after Roger N. Shepard who discovered it in the 1960s. Shepard showed that using basic additive synthesis it's possible to create the illusion of a continuously rising or descending chromatic scale. The term circular pitch was used because, although the scale sounds as if it is moving in one direction, in fact, after twelve steps it returns to where it started. For more info see Wikipedia.
Endless Tone can be used to synthesize classic Shepard/Risset tones. It can also be used as a ring modulator either using an internal sine wave or the audio input for the carrier signal. Endless Flanger is a circular pitch (barber-pole) flanger - instead of flanging up and down the frequency spectrum, it appears to continuously flange in one direction. Endless Phaser works in the same way but rather than using delay lines, it uses filters to produce its effect. Endless Shifter provides a further variation by using pitch shifting to impose the illusion of circular pitch on the source material.
The Endless Series cost £15 for the bundle (Endless Tone is actually free) and is available for Windows and Mac OS X in VST, AU and RTAS formats via the Pluggo runtime.