Digital technologies provide many opportunities to engage the interest and attention of users of all ages. A central question for the designers of these systems is what aspects of user interaction do they want to encourage and emphasize. In this talk, I present several research projects in which I designed digital systems to motivate user participation and collaboration. These projects include a digital living media system that engages child users though the dynamics of caring and responsibility and a Do-It-Yourself (DIY) open-source communication board for non-verbal users. For each project, I describe how I worked closely with various stakeholders including children, parents and teachers. I conclude with reflections on how to design digital system to support human agency and participation.