We present a large, free, French corpus of online written conversations extracted from the Ubuntu platform's forums, mailing lists and IRC channels. The corpus is meant to support multi-modality and diachronic studies of online written conversations. We choose to build the corpus around a robust metadata model based upon strong principles, such as the "stand off" annotation principle. We detail the model, we explain how the data was collected and processed-in terms of meta-data, text and conversation-and we detail the corpus' contents through a series of meaningful statistics. A portion of the corpus-about 4,700 sentences from emails, forum posts and chat messages sent in November 2014-is annotated in terms of dialogue acts and sentiment. We discuss how we adapted our dialogue act taxonomy from the DIT++ annotation scheme and how the data was annotated, before presenting our results as well as a brief qualitative analysis of the annotated data.