Vienna (also called Vienna 1 or Vienna1) is an RNA structure predicting algorithm. It is the energy model that many Eterna puzzles and labs run on.
Vienna 1 is distinct from Vienna 2. Vienna 2 was made by the same group that made Vienna 1 but features updated energy predictions.
Vienna was made by the Theoretical Biochemistry Group within the Institute for Theoretical Chemistry at the University of Vienna.
A paper discussing the Vienna RNA secondary structure server was published in 2003.