Once upon a time in ancient Mongolia, the nomadic horse tribes began fermenting mares' milk to make a drink called airag, a product similar to the drink we know as kefir. At some point, they started taking this fermented mares' milk and distilling it to make a stronger drink known as arkhi. We can't say for sure when this bev-olution took place, but most likely some time after their Russian neighbors started making vodka around 700 or more years ago. While Happy Hour City says that arkhi is the type of drink you're most likely to be introduced to should you get a private invite to visit someone's yurt, this is the 21st century, and of course some commercial distillers have started producing the stuff.
According to Wine Style Online, one such brand, simply called Arkhi, bills itself as a Mongolian vodka and is a product of the APU Company. The drink is said to have a whey-like flavor, or else to taste like honey-flavored skim milk. The one thing we don't know, however, is whether the milk that goes into this drink comes from mares, cows, or some other beastie. The APU website might have more information to offer, but the website's English translation feature was somewhat limited in scope –- which would also be a more than generous way to describe our own knowledge of the Mongolian language.