After the very good reception of the first three issues, we are proud to present the fourth issue of “ST-OPEN”, an internationally-reviewed, multidisciplinary scientific journal published by the University of Split. ST-OPEN is an open-access journal that is available to students and teachers from the University of Split, as well as other universities in Croatia and around the world. In this issue, we continue our author-helpful policy of transforming graduate theses into scientific papers and providing translation services into English at no cost to the authors. All articles are published in diamond open-access format on a continuous basis using the online first publishing principle, which allows readers to access articles well before the entire volume is completed.