The Miracle ME72 Yogurt Maker is the only unit of its kind (that I know of at least) designed especially for making yogurt in a milk carton. Whether this is inspired design or something else entirely, I'll let you be the judge.
This kitchen appliance will make 1 quart of yogurt in 8 to 12 hours. Incubation takes place in the milk carton inside the unit. It comes with and instruction manual including some recipes and a one year warranty.
The main idea behind using the milk carton is that most milk that you buy from the sore has already been pasteurized and because you're leaving the milk inside the container in which you purchased it, the risk of infection from a rogue bacteria strain is minimized which in turn means that you can proceed without the need to boil your milk. This is one of the main criticisms leveled at the more conventional machines - that there is too much fuss in heating up the milk first then allowing it to cool to the correct temperature before adding the yogurt starter culture.
Miracle Milk Carton Yogurt Maker reviews have been mixed. Some customers said they had trouble getting decent results with this unit. They said the heat was not maintained at a high enough level to ensure adequate fermentation within the incubator, having tested it with a cooking thermometer. However, other customers really liked it. They cited the ease of operation - not needing to boil the milk before use as well as just putting the whole milk carton in the machine as major positives.
I've seen the Miracle model ME72 selling anywhere between $30 and $40 so make sure you shop around before you buy.
Read more about the Miracle yogurt maker range.