A serial fanfiction story begun by one author, then added to by other authors chapter-by-chapter or section-by-section, until the story reaches a mutually agreeable ending. Each chapter is usually contained within a post on a message board like PPMB or SFMB. Writers add to the story either at whim, when a good idea strikes them, or in designation rotation. There is usually no overall editor or moderator, so the story can progress with startling turns and twists in plot, sudden losses of major characters, equally sudden additions of new characters, and wild changes in setting.
The chain novel is a round robin in which chapters or sections are written in sequence by authors who have mutually agreed to keep the story going, each section elaborating upon and fusing with the parts before it. A non-Daria example of a chain novel would be Naked Came the Manatee, an action-adventure comedy novel created in the 1990s by a group of famous Florida-based writers (Dave Barry, Elmore Leonard, Edna Buchanan, etc.). Reviews of the novel on Amazon.com reveal many of the inherent pitfalls as well as the attractions of attempting such a story. Conflicts between various writers over the story's direction and anger over the loss of favorite characters are major problems to be faced in the writing.
The format for the chain novel was successfully used in Daria fanfiction ("successfully" in the sense that it was the only round-robin tale to ever be completed) with "Evil Daria Vignettes," which appeared on PPMB. The serialization ran from September 2007 to January 2008.
A mosaic novel, saith Wikipedia, is one in which the chapters or sections are written by different authors who share the goal of telling a linear story start to finish. However, each chapter is written from the viewpoint of a different character or being and is also written in a distinctive style. No Daria round robin has been completed that perfectly reflects these points, but changes in style and perspective are expected with round robins.
For comparison, see chimera.
Other Round Robins
"Fandemonium," though incomplete, is often referenced in other Daria fanfics as a TV series with which many of Lawndale's teens are infatuated. "Fandemonium" features various fanfiction writers in an over-the-top melodrama with science-fiction elements. "Daria's Popular" is perhaps the oldest round robin, begun in July 2005.