A World of Darkness chronicle is what other game systems call a campaign: a series of gaming sessions using the same characters and settings in order to create a larger ongoing storyline.
Chronicles played through Internet Relay Chat, a real-time client-server chat system. Although IRC requires players to be online at the same time to interact, many IRC channels are open 24 hours a day to provide flexible gaming schedules.
Chronicles played through posts to web-accessible message boards. Like play-by-e-mail games, message board chronicles are popular because they allow for asynchronous play -- players don't have to be online at the same time to play together.
Chronicles that require the use of a web browser to access web-based chat rooms for most of their roleplaying sessions. (Many such chronicles use message boards or e-mail for additional roleplaying, but none of the chronicles here could be played without a browser capable of accessing the chat rooms.)