jack_mixer is a GTK JACK audio mixer app with a look similar to its
hardware counterpart. It has lot of useful features, apart from being
able to mix multiple JACK audio streams. It is licensed under GPL
version 2 (or later).
https://rdio.space/jackmixer/
https://rdio.space/jackmixer/tarballs/jack_mixer-11.tar.gz
(transitioned from
gna.org, that was shutdown in 2017)
Changes in version 11?
----------------------
Latest release was on April 27th, 2014, this release brings the much
required port to both Python 3 and GTK 3, as well as audio enhancement
by spreading out volume transition over a period of time to reduce
discontinuities.
Those contributions are from Daniel Sheeler, who deserves all the
thanks.
Enjoy,
Frederic