This volume contains the technical papers presented at three workshops collocated with the 2020 edition of the Software Technologies: Applications and Foundations (STAF) federation of conferences on software technologies. The STAF conferences, satellite events and workshops bring together leading researchers and practitioners from academia and industry to advance the state of the art in practical and foundational advances in software technology. They address all aspects of software technology, from object-oriented design, testing, mathematical approaches to modeling and veri cation, transformation, modeldriven engineering, aspect-oriented techniques, and tools. Before the COVID-19 pandemic exploded, 11 workshops were accepted and planned to be celebrated with STAF 2020. Due to the pandemic, STAF 2020 had to cancel all its physical activities, which were intended to take place in the premises of the Western Norway University of Applied Sciences (Bergen, Norway) from June 22 to June 26, 2020, and new arrangements had to be made. Three workshops decided to go ahead and were celebrated virtually as part of STAF 2020. These workshops are: 1. 1st International Workshop on Modeling Smart Cities. Organizers: Ludovico Iovino, Manuel Wimmer and Juri Di Rocco 2. 4th International Workshop on Model-Driven Engineering for the Internetof-Things. Organizers: Nicolas Ferry, Federico Ciccozzi, Manuel Wimmer, Arnor Solberg and Sebastien Mosser 3. 5th International Workshop on Open and Original Problems in Software Language Engineering. Organizers: Anya Helene Bagge and Vadim Zaytsev We would like to thank the workshop organizers; whose hard work, despite the di culties and challenges, made their events successful. Thanks to the local organizers of STAF 2020 for their trust and support. Finally, we would also like to thank all the participants and people who have contributed to the events as well as the respective Program Committee members and external reviewers who carried out thorough and careful reviews.