Hackathons have become a popular tool for bringing people together to imagine new possibilities for technology. Despite originating in technology communities, hackathons have now been widely adopted by a broad range of organisations. This mainstreaming of hackathons means they encompass a very different range of attendees and activities than they once did, to the extent that some events billed as hackathons may involve no coding at all. Given this shift away from production of code, they might instead be seen as an increasingly popular participatory design activity, from which designers and researchers in HCI can learn. Through fieldwork at six hackathons that targeted non-technical communities, we identify the types of activities and contributions that emerge through these events and the barriers and tensions that might exist. In doing so, we contribute a greater understanding of hackathons as a growing phenomenon and as a potential tool for participatory research.