Johannes Doerr

Midiflow - MIDI router/processor/sync clock

Paid

Midiflow allows you to send MIDI from app to app in a similar way to what you already do with audio.

iMIDIPatchbay

Paid

iMIDIPatchbay lets you organize your whole MIDI setup from one central point.

Midiflow Splitter (Audiobus)

Paid

If you play your synth apps with an external keyboard, Midiflow Splitter is an essential tool for you.