Ringing transient envelope generator
SLY GROGAN is an envelope generator based on the design in Electronotes #86.
It can produce a wide variety of different envelopes and bursts, perhaps most interesting is the ability to have the envelopes ringing after the attack stage. It also works well as a voltage controlled LFO, tho the module is neither a LFO nor a regular ADSR.
https://www.nonlinearcircuits.com/modules/sly-grogan
Available as an assembled module and as a DIY project.
This module is currently available.