Rabāb used to be a term for any stringed instrument.
rabāb or rabābah, an Arabic fiddle in the 10th century. Parent of the medieval European rebec or rubebe (11th-18th century Mediterranean/Balkans) and lira (like the lyre?) The ancient rabāb was the ancestor of almost all European bowed instruments. It had a membranous belly, 2-3 strings, and narrow neck. Its range was about an octave.
Large rebab, more range than the ancient rabab. (similar instrument - kamanche or khomanche) Iraqi and Bedouin - joza, variant with coconut-shell soundbox.
Central and East Asia
The more western, the higher pitched the instrument (?).
Huqin (instrument family) - Chinese variant
Morin khuur - in Mongolia
Kyrgyztan - kobyz
Mughal Empire The seni rabab - wood body with resonator and six strings, no frets and traditionally no sympathetic strings.
Kabuli rabab (Afghan) - hollow wood body with gut or nylon strings.
The modern r*bab usually has a small, rounded body, covered with a membrane on the front. Long thin neck with pegbox, and no more than three strings. No fingerboard, spike to rest it on ground during performance. Played held upright, resting on floor or player's lap.
Rebab is a component of gamelan, as a bowed two-stringed lute made of wood or coconut shell covered with hide. Usually two per gamelan ensemble, one for each scale (pelog and slendro). Sometimes used in healing rituals.
Rest of Southeast Asia
Used for healing rituals in eastern Malaysia.
Thailand: saw sam sai, three-stringed spike fiddle (and related saw u and saw duang)
Cambodia: tro Khmer, coconut-shell fiddle
Tuva: byzaanchy and igil, spike fiddles
China: Yehu, diyingehu, erhu, erxian - related, bowed long-necked spike fiddles with two or three strings
Bulgaria: gadulka (related to Cretan lyra, which is entirely unrelated to lyre)
== Notes ==
Rabab - original ancestor.
Rebab - used in gamelan, general name for r*bab in most resources.
Robab or rubab - originated in Afghanistan. (Britannica 1911: The pear-shaped instrument...with strings plucked by the fingers, — the lute of the 6th century A.D., — is seen first on a frieze from Afghanistan.) Possibly diverged from here. Short-necked lute with three melody and 2-3 drone strings, usually nylon.
Rabob - Central Asian single-piece instrument?
https://www.metmuseum.org/toah/works-of-art/89.4.403/ (Algerian rebab)
https://www.wdl.org/en/item/10826/ (Central Asian rebab, c. 1880)
http://collections.nmmusd.org/Gamelan/9870/Rebab9870.html (Javanese rebab, used in gamelan)
https://research.britishmuseum.org/research/collection_online/collection_object_details.aspx?objectId=3439763&partId=1 (Central Asian rabob, Xanthus)