Voltage controlled Slew limiter AKA Lag Processor. Black panel

A Slew limiter is a device that smoothes an incoming signal, limiting the maximum rate of change of the output voltage per unit of time
It is widely used applying it to pitch CV to obtain portamento but can be very useful in other applications like convert a gate signal into a basic envelope
This module have independent time controls for rising and falling voltages, each of them with his own CV.
Also you can change the response from linear to logarithmic with a dedicated potentiometer.

http://www.befaco.org/en/vc-slew-limiter/