"Since Euler's development of the Tonnetz in 1739, musicians, composers andinstrument designers have been fascinated with the concept of musicalisomorphism, the idea that by arranging tones by their harmonic relationshipsrather than by their physical properties, the common shapes of musicalconstructs will appear, facilitating learning and new ways of exploringharmonic spaces. The construction of isomorphic instruments, beyond limitedsquare isomorphisms present in many stringed instruments, has been a challengein the past for two reasons: The first problem, that of re-arranging noteactuators from their sounding elements, has been solved by digital instrumentdesign. The second, more conceptual problem, is that only a single isomorphismcan be designed for any one instrument, requiring the instrument designer (aswell as composer and performer) to ""lock in"" to a single isomorphism, or tohave a different instrument for each isomorphism in order to experiment. Musix(an iOS application) and Rainboard (a physical device) are two new musicalinstruments built to overcome this and other limitations of existing isomorphicinstruments. Musix was developed to allow experimentation with a wide varietyof different isomorphic layouts, to assess the advantages and disadvantages ofeach. The Rainboard consists of a hexagonal array of arcade buttons embeddedwith RGB-LEDs, which are used to indicate characteristics of the isomorphismcurrently in use on the Rainboard. The creation of these two instruments /experimentation platforms allows for isomorphic layouts to be explored in waysthat are not possible with existing instruments."