In a European context, in which it is increasingly clear that the so-called 21st Century Competencies are essential to understand and peform in the world today, we find groups that for various reasons do not participate in activities aimed at developing these competences. Since 2017, the European Commission (after public consultation) highlighted the key importance of 3 competences: mathematical competences, literacy and digital competencies.Some key data allowed profiling the main target group of the project: adults. For example, about 55 million adults between 15 and 65 have difficulties with reading-writing in their own language; 24% of the EU population have a level 1 or below in maths (on the five-point scale); and 44% of Europeans have no basic digital skills.On the other hand, the technological innovation that has broken into the last decades implied structural changes that decisively influenced virtually all areas of our lives. Technology changed the way we relate with others, our habits and lifestyles, our way of understanding and enjoying leisure time and also our way of learning and teaching.Thus, the App4skills project focused on the development of a web application that allows, in a playful-educational context, to improve the basic skills of European adults in mathematics, literacy and digital skills.The project focused its activities towards the fulfillment of the following objectives:- Improve creativity and develop in students the ability to create new problems / activities, ask questions and share relevant ideas.- Improve students' perception of learning mathematics, improve their literacy skills and promote their digital skills, increasing their interest, motivation, flexibility and perseverance, and correcting negative attitudes traditionally linked to lack of trust, low self-esteem or the anxiety that can be generated by formal learning settings.- Prepare students for continuous and autonomous learning, developing critical thinking and promoting equity, social cohesion and active citizenship.- Promote the professional development of adult trainers in basic skills, providing them with a new tool for use in informal and non-formal contexts.The project implementation counted on specialists from five countries (Spain, Finland, Poland, Italy and Turkey), members of the partners' work teams, but also from other local, national and European entities linked to them. Professional networks were activated and dinamysed to obtain valuable feedback for the project.In addition, the project counted on the direct participation of 391 people in the phases of testing of the prototype and in the presentations made in the different multiplier events. All of them representatives of the project's target groups: adults and their trainers.The web application was developed in several phases, which we could summarize in 3: design and development of the prototype, testing with real users, adaptation and inclusion of improvements for the development of the final version.It is worth noting the wide participation of users in the testing phase (159 people, of which 123 were adults and 36 trainers), and the positive feedback received. As an example, we can highlight that 91.82% of the participants considered that the webapp meets their expectations and 91% believed that its design is attractive.In addition to the direct positive impact on these users, the project continuously carried out networking and dissemination actions with the objective of gathering the interest and collaboration of other entities for the use of the webapp, once the project is finished. In this sense, some interesting connections have already been made, and the data recorded in the web application show that the number of activities has increased from 300 published by the partners to 342, which is a sign of their use by third parties.