There are various sorts similar to the ones found on Urth.
Czehar
Musical instrument consisting of a flat, oblong box, having 8 strings, it is held across the lap when sitting
cross-legged and is played with a horn pick; similar to a Japaniese koto
Flute
Same as Urth flute and the players always keep them polished
Kalika
A six-stringed instrument; it, like the czehar, is flat-bridged and its strings are adjusted by means of small wooden cranks; on the other hand, it less resembles a low, flat box and suggests affinities to the banjo or guitar, though the sound box is hemispheric and the neck rather long; it, too, of course, like the czehar, is plucked
Kaska
A small hand drum
Notched stick
Played by sliding a polished tem-wood stick across its surface
Tabor
A small drum
Tambourine
Bits of metal on wires; gourds filled with pebbles and slave bells mounted on hand rings
Zills
Finger cymbals
Some interesting quotes from the scrolls:
I have never seen a bowed instrument on Gor; also, I might mention, I have never on Gor seen any written music; I do not know if a notation exists; melodies are passed on from father to son, from master to apprentice.
--Nomads of Gor, pg 153
Among Gorean musicians, incidentally, czehar players have the most prestige; there was only one in this group, I noted, and he was their leader; next follow the flutists and then the players of the kalika; the players of the drums come next; and the farthest fellow down the list is the man who keeps the bag of miscellaneous instruments, playing them and parceling them out to others as needed. Lastly it might be mentioned, thinking it is of some interest, musicians on Gor are never enslaved; they may, of course, be exiled, tortured, slain and such; it is said, perhaps truly, that he who makes music must, like the tarn and the Vosk gull, be free.
--Nomads of Gor, pg 154