Official forum
Atlas Games operates an official discussion forum for Ars Magica, located here.
The forum is a good place to ask questions about the rules and setting that are not covered by the Project:Redcap FAQ. It's also a good place for general discussion of Ars Magica and for sharing and discussing new characters, spells, and the like. The official forum also hosts online play (in a play-by-post format).
In addition to many creative and dedicated Ars Magica players, several of the game's authors, its publisher, and its editor are active on the official forum.
Since the forum opened in 2005, it has gradually supplanted the Berk List as the primary (but not exclusive) forum where the Fan Community discusses Ars Magica.
Legacy Page
The history of this page before July 22, 2012 is located at Legacy:official_discussion_forum.