The Korg DS-8 is a 4-operator digital FM synthesizer with a 61-key keyboard. It was released in 1987 and sounds similar to many of Yamaha's FM synthesizers because it is based on the YM2164 (OPP) chip, which is found in the Yamaha DX21, DX27, and DX100. It has 8 notes of polyphony and is 8-part multitimbral. It has 100 patch memories and 10 performance memories and basic built-in digital effects (delay, flange, chorus, and double). It has a joystick control for pitch bend and modulation and its low-frequency oscillator waveforms are saw, triangle, square, and sample & hold. It lacks an arpeggiator or sequencer.
The DSCU-400 library card adds another 100 patches to the Korg DS-8.
A little-known secret of this synthesizer is that you can put it into "glitch mode" by overloading the MIDI buffer when sending sysex data. This will result in a garbled display, strange behavior, and some incredibly strange glitch sounds, which may or may not be desirable depending upon your genre of music. However, we do not know whether it is easy or even possible to recover from this mode.
The 707 was another 4-operator FM synthesizer released by Korg.