After a lot of digging through pages on Google, i came across this gem -
http://www.fretlesszithers.net/gz_home.htm
Created by Kelly Williams, it is a nice collection of information about fretless zithers, guitar-zithers, chord or chorded-zithers and all the other names these things go by.
I have seen plenty of minimum-effort websites but this one is especially not pretty
The content however is delightful, Kelly if you are out there somewhere, please know that not all heroes wear capes and know how to write HTML code, but you are appreciated anyway.
Everyone else - Please go see his site.