This app is capable of calculating the optimal flexible and more efficient phase II designs based on discrete conditional error function (incl. over- and underrunning) as proposed by Englert and Kieser (2012, 2015). To use this app, please specify the input parameters in the left panel and press 'Calculate'. After the calculation is complete, the optimal discrete conditional error function is presented in the right panel. Please note that depending on the selected parameters the calculations may require some time until they are completed.