Cos4Cloud is a European Horizon 2020 project to boost citizen science technologies. One of the biggest challenges of citizen science is the quality of data, as well as maintaining the citizen observatories used to collect this data. Cos4Cloud is addressing these challenges by developing ten technological services to improve citizen science platforms, also known as citizen observatories, to help them boost the quantity and the quality of observations and, finally, to help ensure their long-term viability.