New methods and technologies for engaging future users and other stakeholders in participatory (design) processes are being developed and proposed. Increasingly, researchers refer to co-creation in order to capture such approaches. However, how co-creation is being framed and understood across domains differs substantially. To better understand co-creation in computing, we conducted a literature review of all papers in the ACM Digital Library with co-creation or co-create in their abstracts. After an initial screening, we retained 62 for further analysis. We introduce a framework to analyze different notions of co-creation, distinguishing between co-creation target audiences, the roles of co-creators, the role of technology (as means or objective) and its results. We discuss the adoption of co-creation in domains such as learning, business, arts & culture, health, and the public sector. This paper contributes to the understanding of different approaches and conceptualizations of co-creation in computing and puts forward an agenda for future research.