Rotovap is short for rotary evaporator. They have been used in chemistry labs for decades and slowly, the world of gastronomy adopted them to make bespoke flavours. For spirit makers and distillers, they represent a unique form of distillation apparatus because they are capable of distilling at very low temperatures.
The reason they are able to do this is that rotovaps work under vacuum. By taking out the atmospheric pressure out from within the sealed system, ethanol can be separated from the liquid in the flask at temperatures as low as 20C. Gin makers use this feature in particular, in order to capture delicate notes from floral and citrus botanicals that would otherwise be lost, cooked or stewed due to the need to heat up in a traditional still.