Tea and coffee don't have to be sweet either, and there are lots of cold versions of those.
Kvaas contain alcohol, doesn’t it?
I think only as much as kombucha, not enough to cause a buzz
I did almost mention jaljeera, but thought that might be a bit niche. It is also often sweetened though. I've never known not-sweet lassi though? Salted lassi is still sweet underneath, like salted caramel, ime. We could count it with the sweet-ish milk drinks, anyway.