Stompwatch 1.1 -- Tamper Time! (video)
"Stompwatch is a virtual MIDI pedal board app; it runs on iOS 7 and newer, and makes it easy to control synthesizers and sequencers. There are ten pages of controls, and each page can specify any number of MIDI destinations. On each page, there are ten pads; these can be configured to send MIDI notes, chords, or MIDI program change or control change messages. You can use MIDI over Bluetooth to allow one iOS device to control another.
A new feature of version 1.1 is support for the ION iCade. The iCade is a game controller, with eight physical buttons and a joystick; you can use this to trigger pads in Stompwatch. Because the iCade is inexpensive and durable, you can use it to create a MIDI foot controller. The iCade is also easily hackable.
Stompwatch also supports Audiobus Remote and the Apple Watch."