Eva Kingma, flutemaker based in The Netherlands, established her company in 1975. They specialize in manufacturing low flutes, and have developed the innovative “Key-on-Key mechanism” and the patented Kingma System® . https://www.kingmaflutes.com/mySite/index.html
Specializing in making “lower” sounding flutes including Alto, Bass, Contra-Bass and Sub-Contra Bass, she has made an open hole alto flute, as well as a quarter-tone, open hole alto, bass and contrabass. In a collaboration with Bickford Brannen, a full quarter-tone C flute with the Kingma System is available from Brannen Brothers Flutemakers, Levit Flute Company and Sankyo Flutes.
Check out her website for a schedule of flute events around the world in which she is involved.