Cross-platform development frameworks allow producing a single codebase for an app targeting web browsers and native mobile operating systems. However, detractors stress their limitations in accessing platform-specific features or achieving optimal performance compared to native platform development. Although interest in cross-platform development has increased recently, few case studies are published on using them, often on toy examples. Therefore, it is important to provide sound evidence on the usage of a cross-development platform for a full-fledged app development case study, from requirements specification to quality assurance, using well-understood standard modeling notations (UML and BPMN). This case study is about IscteSpots, a gamified app developed in the scope of Iscte’s commemoration of its 50th anniversary, to promote its heritage and history. One of its components provides publicly organized access to a chronological corpus of the university’s past and is available on web browsers and on/ Android and iOS smartphones. Another component, specifically targeted to smartphones, implements a contest with gamification strategies, specially targeted to the current community members (students mostly, but also teaching and administrative staff). Development went through several iterations, including validations with groups of users that were instrumental in the app’s continuous improvement. The vast majority of the suggested changes had repercussions at the GUI level, that had to be propagated to the web, Android, and iOS platforms. The agility achieved by generating versions for the three target platforms, without noticeable degradation of execution efficiency and requiring only minor adaptations, amply proved the advantage of using a cross-platform framework.