Context: Gamification is an emerging subject that has been applied in different areas, bringing contributions to different types of activities. Objective: This paper aims to characterize how gamification has been adopted in non-educational contexts of software engineering (SE) activities. Method: We performed a Systematic Mapping of the literature obtained from relevant databases of the area. The searches retrieved 2640 studies (published up to January 2020), of which 548 were duplicates, 82 were selected after applying the inclusion and exclusion criteria, and 21 were included via the backward snowballing technique, thus reaching a total of 103 studies to be analyzed. Results: Gamification provided benefits to activities like requirements specification, development, testing, project management, and support process. There is evidence of gamified support to some CMMI 2.0 Practice Areas. The most commonly used gamification elements are points and leaderboards. The main benefit achieved is the increased engagement and motivation to perform tasks. Conclusion: The number of publications and new research initiatives have increased over the years and, from the original authors' reports, many positive results were achieved in SE activities. Despite this, gamification can still be explored for many SE tasks; for the addressed ones, empirical evidence is very limited.