Pierre pointed me to this nice example of communication tool which makes explicit the communication context. This is greatly related to my research agenda as I am studying how these systems affect user performances in a task setting.

Communication is always embedded in a specific communication context. The participants build up knowledge using learning material, they discuss a draft or react to a message in a discussion. Existing chat systems do not pay attention to this context. The participants have to re-construct the communication context on their own. This is timeconsuming and leads to misunderstandings.