Recent research has highlighted the emergence of “alternative social media” platforms. Developed by open source communities with non-commercial goals, these platforms can offer more expansive participatory cultures than corporate platforms. However, such platforms also involve new kinds of participatory challenges, such as requiring high technological literacy. This article examines the complexity of enacting participatory cultures by drawing on an ethnographic study of Scuttlebutt, a decentralized social media platform being developed by an open source community. This examination focuses on three key features of participatory culture as enacted on Scuttlebutt: varying modes and sites of participation; reflexivity about who is participating and how; and an evaluation of limits to participation. It also considers the challenges that arise from Scuttlebutt’s approach and how these highlight the profound difficulty of trying to enact fuller models of participatory culture. From these findings, we argue that Scuttlebutt provides an important example of the experimentation that alternative social media platforms are conducting around open, democratic modes of socio-technical organizing, and note that this experimentation raises important questions about how we conceptualize participation and the future of social media.