Generalized keyboard

They were introduced by Robert Bosanquet in the 1870s, and since the 1960s Erv Wilson has developed new methods of using and expanding them, proposing keyboard layouts (and some notations) including any scale made of a single generator within an "octave" (or more generally, period) of any size.

Arthur von Oettingen's 1914 Omnitonophonium harmonium has keys similar to Bosanquet's, but which aren't undercut (like Jankó's 1883 patent for his 12-tone keyboard).

Arthur Fickénscher patented a keyboard in 1941 with rectangular keys overlapping in 12 staggered diagonal rows each representing the same named tones.

Scott Hackleman and Erv Wilson designed a 19-tone generalized keyboard clavichord with oblong hexagonal keys in 1975, and marketed it as a kit.

[2] Michel Geiss, fr:Christian Braut and Philippe Monsire built the Semantic Daniélou, a 36-tone (out of 53 just intonation notes listed in the book "Sémantique Musicale" by Alain Daniélou) electronic instrument, on behalf of the author, using staggered square key button keyboards from two Cavagnolo Midy 20 master keyboards, where each parallel row of keys offers a transposition by one comma.

Harold Fortuin's 1994 Clavette midi controller uses straight alternating rows of switches which can be customized for different tunings by programming and with key overlay sheets.