Through a detailed account of the history of online chat devices, this article shows the emergence, over time, of two distinct interactional formats underlying these social media. They may be captured by two generic metaphors of synchrony: "conference" (a gathering in a virtual place where unfocused interactions and group sociability occur) and "copresence" (where practices are centered on the sustainment of contact between individuals who know each other). Internet Relay Chat (IRC) appears as the archetype of the conference format. This notion of chat involves the existence of a relatively persistent shared space--conjured up by various specific metaphors: room, channel, and so on--inside which users get together and through which they are able to find other users, with whom they may weave electronic social ties that may possibly lead to offline relationships. The other format is associated with instant messaging (IM) devices, on the model of "ICQ" software. Although there seems to be a decline in interest for devices based on the former format, those based on the latter benefit from a growing popularity, possibly indicating deeper sociological implications. (Contains 58 notes.)