In the recent years, due to the emergence of new models of production based on collaboration, collaborative writing tools started to be increasingly used by various communities. Due to great variety of groupware software, there is the need of criteria for discriminating the working modes supported by these tools. In this paper we propose a new model for the classification of collaborative writing tools. Based on our model, we categorize most popular existing collaborative tools. We also propose novel working modes that are not adopted by existing tools and that improve the process of collaboration.