Hi! Here (https://gitlab.com/iurie/geonkick) I have developed a free software/GPLv3 percussion synthesizer that can synthesize kick drums, snares, hit-hats, shakers, claps, steaks. For now it is only a standalone application, no LV2 plugin for now.
It works only with Jack server for now. Percussion graph can be seen in real time when modifying the synthesizer parameters or envelopes, and can export to WAV, FLAC, Ogg, save/open preset. It has one MIDI (key velocity sensitive) input and two audio outputs.
I hope someone will find it useful. There are some examples presets that can be opened and play with under the directory examples.
In the version 2.0 I am planning to add more functionality, redesign the GUI, and improve the DSP part in order to enable LV2 functionality.