Available as an assembled Module and as a DIY project.
This Module is currently available.
Lag processor / slew limiter
The ASM307 Lag Processor is an implementation of Harry Bissell's Morph Lag circuit.
The ASM307 has independent controls for setting the rise and fall times, and a shape control to vary the response between linear and logarithmic.
The ASM307 has the following controls:
UP: sets lag time for positive (increasing) voltages.
DOWN: sets lag time for negative (decreasing) voltages.
SHAPE: sets the response from linear to logarithmic.
https://www.elby-designs.com/webtek/panther/asm307-lag-processor/asm307.htm
These merchants probably sell this module. Huh?