Gamification refers to approaches that apply gaming elements and mechanics into contexts where gaming is not the main business purpose. Gamification principles have proven to be very effective in motivating target users in keeping their engagement within everyday challenges, including dedication to education, use of public transportation, adoption of healthy habits, and so forth. The spread of gameful applications and the consequent growth of the user base are making their design and development complexity to increase, e.g., due to the need of more and more customized solutions. In this respect, current state-of-the-art development approaches are either too close to programming or completely prepackaged. In the former case, domain and gamification experts are confronted with the abstraction gap between the concepts they would like to use and the corresponding implementation through coding. In the latter situation, customization opportunities are remarkably limited or require again hand-tuning through coding. In both scenarios, programmer tasks are tedious and error-prone, given the intrinsic characteristics of gamified applications, which are sets of rules to be triggered as a consequence of specific events.