C3LLO-REO is the mobile app for the e-learning platform C3LLO for the Renewable Energy Online curriculum at the Carl von Ossietzky University of Oldenburg. It provides mobile access to C3LLOs main tools, such as forums, messages, appointments, and learning content. Please note that this app requires valid user credentials for C3LLO at https://en.reo.uni-oldenburg.de.