JVC ECA-102
(1970s)

I admit a trivial weakness for such looky-looky devices.
Fairly useless, completely useless that is - but so much more exciting than the latest SACD improvement or next lossless format.

The ECA-102 is a reverberation amplifier (solid-state - no spring reverb here) that adds depth and color to sound reproduction in two channel... or four channel ! A radar screen displays green and white kaleidoscopic patterns that blip to show sound dispersion and reverberation levels.
Adding your own microphone is possible so you can sound like Star Trek's Voice of Klingon speaking right from the next galaxy. Tape monitoring and dubbing are also possible to properly record and / or dub said Voice of Klingon.

Note : an overdose of Klingon is bad for your health and can operate irreparable damages on your nervous sytem.

(but so much fun)