The viola da Gamba is one of the viol family. The others aren't "da Gamba" - Gamba is Italian for knee and refers to the instrument being held between the knees the same way up as a cello. The others are something like the treble and tenor viol and played the same way up as a violin and viola, and I believe the bass viol is is the forerunner of the modern double bass.

(also the viola d'Amore, not sure where that fitted in)

But it's quite true that the viol family are fretted instrments!

Anahata