The SweeTango is a hybrid between the Honeycrisp and the Zestar. I don't recall seeing the Zestar apple around here - I think it's more of a local apple in Minnesota.
All three of these apples - Honeycrisp, Zestar and the SweeTango (sweet and tangy) were developed at the University of Minnesota. The picture below of some Sweetango apples on a conveyor belt is from Wikipedia.