1. West Georgia generally; 2. certain isolated villages of European Russia, near the Ukrainian border, notably in Briansk, Kaluga and Kursk -- also isolated areas of the Komi Republic, Serbia, Rumania, and Lithuania ("hooted" vocalizing associated with panpipe playing, as reported by Olga Velitchkina and Ruta Zarskiene); 3. the Appenzell region of the Swiss Alps; 4. the "Tralalero" tradition of Liguria, in Northern Italy; 5. the "highland" region of Eastern Lithuania (associated with the sutartine tradition); 6. the Algarve region of Portugal; 7. medieval Wales (as inferred from the writings of Geraldus Cambrensis); 8. certain forms associated with medieval liturgical music, such as the rotus, rondellus, chace and caccia -- and practices such as the round, canon, stimmtauch and hocket/interlock, thought by some medievalists, with good reason, to have originated in oral traditions.
While it could certainly be argued that each of the above represents a unique, independently developed musical practice, such an interpretation seems unlikely, for several reasons. As with traditional polyphonic vocalizing generally, the contrapuntal type appears in almost all cases to be found in remote, isolated pockets, well off the beaten path, associated with other traditions generally thought to be ancient or archaic, often centered in the sort of mountainous or heavily forested areas where we would expect to find the survivals of any region's oldest traditions. In addition, many of these contrapuntal practices are linked by other highly distinctive musical features, such as: the presence, either common or sporadic, of "resultant" effects, produced by hocket/interlock, stimmtauch or both; and the presence, either common or sporadic, of either yodel or falsetto singing (falsetto was singled out by certain church leaders as one of the "excesses" of medieval hocket; falsetto is an important feature of the Tralalero tradition; the vocalizing of the Russian panpipers documented by Velitchkina is "hooted" in a manner very close to yodel; yodel is a common feature of polyphonic vocalizing in the Appenzel and West Georgia; yodel was associated with certain types of "popular" medieval polyphony by Bukofzer).
There are also in many cases strong associations with certain types of instrumental hocket. The panpipers studied by Velitchkina and Zarskiene sing as they hocket together on their pipes. Lithuanian sutartines can be played by hocketing pipe or trumpet ensembles in addition to being sung. Similar ensembles of horns or trumpets have been reported for Russia. Alphorns in Switzerland and elsewhere could have played together in hocketing ensembles at one time (though at the moment this is only a conjecture). There is (or was) an important tradition of panpipe hocket in Georgia. Finally, we have an intriguing quotation from Adam de la Halle associating medieval hocketing with both folksong and panpipes:
Adam de la Halle uses the term in the highest voice of a polyphonic motet. He relates how four young fellows, when they hocket, make percussive sounds faster than the panpipes. They also dance together, beating on the floor while hocketing. ("Quant il hoquetent Plus tost clapetent Que frestel Li damoisel... Et quant il font le moulin Ensamble tout quatre Et au plastre batre En hoquetant" [Tischler, 3:74-6, 4:83-4; Adam de la Halle p. 202-5].) (See http://www.the-orb.net/encyclop/culture/music/hocket.html)