A monophonic, analog synth prototyped by Octave-Plateau during the development of the Voyetra 8. The Voyetra One and Voyetra 8 were envisioned by Octave-Plateau as the first two elements of a system (as can be seen in the advertisement reproduced below). In addition to being a monophonic synthesizer module, the Voyetra One was primarily designed to serve as a programming panel for the Voyetra 8, which did not have enough panel space for all of the system parameters due to its compact, rack panel design.
Once the IBM PC was introduced, Octave decided to write a software patch editor for the Voyetra 8, which presented all of the Voyetra control parameters on the screen, making it easy to create and save sounds to disk. At that point, the Voyetra One was no longer necessary and was discontinued before prototypes were even finished. Octave-Plateau turned away from hardware development after the analog synthesizer market collapsed in the mid-1980s, so whatever other elements were envisioned for a Voyetra family of products never emerged.
Shown below is a Voyetra sales brochure from 1983 showing the Voyetra One is pictured at the top, with the 8 at the bottom, and the VPK-5 keyboard (which played either synth) in between.