The instruments listed here and on the websites linked below follow the principle of isomorphism, the identical or similar appearance of intervals in all transpositions. This means they are key-neutral and scale-neutral. Isomorphism is also found in many alternative notation systems.
Intuitive Instruments for Improvisers (Paul Hirsh) – http://improvise.free.fr/ A website about isomorphic instruments, isomorphic panpipes, Janko keyboards, and more…
Keyboards, Accordions, Button Instruments
Generalized keyboard, a predecessor of the Janko keyboard that accommodates microtonal tunings (invented by R. H. M. Bosanquet, extended by Erv Wilson and others) – http://en.wikipedia.org/wiki/Generalized_keyboard , http://improvise.free.fr/bosanquet/bosanquet.html
Janko Keyboard Layout with two whole tone scale rows
Daskin brand Janko Keyboards (Paul Vandervoort) – http://daskin.com/
Lippens keyboard derived from Janko’s design
Chromatone brand Janko-style keyboards (Japanese company) – http://chromatone.jp/
Chromatone Lite for iPad – http://itunes.apple.com/us/app/chromatone-lite-for-ipad/id382628130?mt=8#
Dodeka Keyboard – http://www.dodeka.info/DodekaEnglish/Instruments.html
The Balanced Keyboard (Bart Willemse) – http://balanced-keyboard.com/
Chromatic Button Accordions – http://en.wikipedia.org/wiki/Chromatic_button_accordion
Musix for iPad – http://www.shiverware.com/musix.html One of the layouts is the Wicki-Hayden.
The DIY Keyboard Project (Drew Wagner) – http://diykeyboard.org Focuses on building alternative, isomorphic keyboards. It is an open-source hardware development project with the goal of making all of the CAD files, microcontroller code, etc. necessary for a hobbyist to build a digital keyboard freely available.
6-6 Colored Traditional (7-5) Keyboard (on this wiki)
Isomorphic Saxophones and Flutes (Jim Schmidt) – http://www.jsengineering.net/
Chromatic harp – http://www.chromatiker.de/Harfenbauer.html (Page in German)
Isomorphic Vibraphone with a Janko-style layout, and three-color pattern (Roy Pertchik) – see Tri-Chromatic Keyboard Pattern