Cittern

The cittern or cithren is a stringed instrument dating from the Renaissance. Modern scholars debate its exact history, but it is generally accepted that it is descended from the Medieval citole, or cytole. It looks much like the modern-day flat-back mandolin and the modern Irish bouzouki. Its flat-back design was simpler and cheaper to construct than the lute. It was also easier to play, smaller, less delicate and more portable. Played by all classes, the cittern was a premier instrument of casual music-making much as is the guitar today. (source)