dsp or other function, programmed to an 8-pin chip on faceplate, swappable
The 4HP eurorack module has a 8-pin DIP socket on the outside like the old Simmons EPROM drums that host an ATtiny45/85 MCU.
Like an Ardcore or Euroduino it can host whatever you program yourself into an ATtiny45/85.
Anything from simple VCO’s, LFO’s and other oscillators to complete drum sounds and complex FM voices.
2 analog/CV inputs with attenuators and 1 cv analog/digital input jack.
1 audio output jack.
It is supplied with the necessary library/core interface for writing any DSP application you want with the Arduino IDE and playing it in your eurorack synthesizer
https://janostman.wordpress.com/2016/04/28/dsp-host-a-4hp-eurorack-attiny85-module/
No info about availability.
$99