One of the few characteristics of Algerian Arabic that are genuinely unique to Algeria isكاش "some, any". At first sight, this rather frequent word must baffle Arabic speakers from other regions, to say nothing of learners of Arabic. However, it turns out to be a quite recent development, completed only in the 20th century, from two well-known Arabic words:كان "there is" (originally "was"), andشي "some, something, thing" (originally "thing"). I've just published a short article examining its usage and development: From existential to indefinite determiner: Kaš in Algerian Arabic (in the Proceedings of AIDA 11 ). Its core findings are summed up in this little graphic:

The center of the image has already been explained above. For the rest, you need to see examples of the five principal functions of kaš. The most central seems to be as an irrealis indefinite determiner, as in:

جا كاش واحد؟ ja kaš waħəd? came any one? "Did anyone come?"

كاش حليب؟ kaš ħlib? any milk? "Is there any milk?"

ماكاش الزهر makaš əz-zhəṛ NegExist the-luck "There is no luck."

كاش ما شريت؟ kaš ma šri-t? any that buy-2Sg? "Did you buy anything?"

كاش ما جا؟ kaš ma ja? any that came? "Did he come (at all, by any chance)?"

However, it can also be used existentially in questions, as in:And, of course, it forms the second half of the extremely frequent negative existential "there is no":In combination with the complementiserما, it yields another two rather surprising constructions:For full details of how Algerian Arabic managed to produce all these functions by combining an existential marker and a quantifier, you'll have to read the article!

A rather similar grammaticalization seems to have taken place in Chinese for yŏu 有; can you think of any other comparable cases?