Citizens around the world are changing their urban environment through bottom-up projects. They are increasingly using digital platforms to come together. From the perspective of smart city research, this form of participation and interaction with city administrations has not yet been researched and defined. In our study we suggest a conceptualisation of bottom-up urbanism participatory platforms and analysed 143 platforms. We identified 23 platforms as our study sample. They vary in their focus from implementation to funding or discussion. Therefor we found a broad range of participation mechanisms. A wide range of employment or voluntary work of staff members was shown. A heterogeneous picture also emerged regarding other characteristics (e.g. funding size, users or number of projects). One thing they have in common is their good cooperation with cities and regional actors.