Part 1: The Hurdy-gurdy
If a violin were gene-spliced with bagpipes, a piano, and a sewing machine, the result might look like a hurdy-gurdy. It uses a rosined wheel to vibrate drone strings, while the melody is played on a melody string using a keyboard. This TED talk explains the instrument nicely.
Part 2: The Nyckelharpa
The nyckelharpa resembles a violin, is carried like a guitar, or lute, and like the hurdy-gurdy, is played with wooden keys that do the fretting. But in place of the wheel it uses a more traditional violin bow. The addition of sympathetic strings give it a very rich sound. In this video, Thomas Roth most certainly does it justice.