Presenting the new Open Cities App Challenge. Open Cities are launching their final round of the Challenges, promoting open innovation at the cities and citizens involvement. Using the more than 2000 datasets opened up by the cities during the project life and the new Hack-At-Home platform introduced, the project challenges will evolve around the problems that big EU cities face related to the management of large tourist flows. Following this new process, developers from all over the world will be guided on transforming their ideas into full working and sustainable apps with the constant help and mentorship of a set of experts in the area of tourism and open data.