MIDI Designer Pro 2
MIDI Designer Pro 2 allows building of custom MIDI control surfaces.
App type: App
App store link: 
Developer: Confusion Studios LLC
Developer AB Forum Handle: @MIDIDesigner
Additional Info
- The scripting language found in the StreamByter AU MIDI processor plugin is available as an In-App Purchase in MIDI Designer Pro 2.
- MIDI Designer Community-Sourced Layouts - a large and ever expanding collection of user made layouts.