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.