sfc (SoundFontCombi) is a midi router designed to mix the sounds of your
sound devices. Up to 8 sounds can be mixed or split. There are  6 MIDI
out ports and 2 MIDI in ports. Up to six different devices can be used
to produce combinations of sounds like some synthesizers.

The connections with your devices are automated. You can load/save your
"mixes" in banks of sounds, and change it via Midi Program Change message
or by the user interface.

This requires fltk.