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.

Features:
* Mix any number of input channels (mono or stereo).
* Control balance and faders with MIDI commands.
* Handle session management with LASH.
* Create as many outputs as necessary.
* Quickly monitor inputs (PFL) and outputs.
* ...