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 or jawza, 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
Kobyz - Kyrgyztan
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. Still seen today, somewhat rare.
The rebec was an instrument played in the Medieval Era (popular from the 13th to 16th centuries). Usually three stringed, bowed, played placed under the chin. Variant of rabab introduced to Europe as Arabs invaded Iberian peninsula.
Byzantine lira, stringed instrument of the early Roman empire, early spike fiddle. Derived instruments still in use today. Ibn Khordadbeh, 9th century Persian hsitorian, described this as equivalent to the rabab. Similar to a pear-shaped rebec. Some lyra variants, unlike ancient rabab, had rear tuning pegs set in a flat peg.
The modern r*bab usually has a small 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. The body can be circular, oblong or box-shaped.
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. The pitch of the instrument is not fixed and usually the higher string is played. Likely was introduced to this region in the 15th century as Islamic influences entered Javanese culture.
Rest of Southeast Asia
Used for healing rituals in eastern Malaysia. Versions of the rebab, similar to the Indonesian gamelan instrument, are present around SE Asia.
Thailand: saw sam sai, three-stringed spike fiddle (and related saw u and saw duang)
Cambodia: tro Khmer, coconut-shell fiddle
Descendants of the rebec and Byzantine lyra continue to be in use today, though the spike in some cases is mostly vestigial.
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)
Greece: Politiki lyra, Cretan lyra
== 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.musicologie.org/sites/r/rabab.html (In French, has a great image collection)
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)