Antonio Poves has published a wonderfully detailed site dedicated to the organistrum, the earliest incarnation of the hurdy-gurdy. Although often thought of as an instrument for two players, Antonio points out that there are examples of instruments for one player, and that the defining characteristic is the location of the keybox (to the side of the body, rather than on top) rather than the number of players. The site is based on his doctoral thesis on the organistrum, which won an award for the best thesis in the area of Fine Art at the Polytechnic University of Valencia in Spain. The site includes information on a number of organistrums that he has reconstructed with the help of luthiers, as well as linked to recordings and videos he has made of the instrument. A very rich site and well worth visiting. Online here.