A complex issue.
Via Crucis: This particular brand of Valentian nonsense first caught on after the Hiems Perpetua, when many former Ostian residents lived in Valentia until the founding of Kellenheim, which maintains a small church.
The Children of Amon: Either a medical diagnosis or the name of an Ostian cult, little is known about either. Scottish_Irony's descent to madness is often blamed on this shadowy minority.
Stition: often mistakenly called the state religion, Stition is a loose mixture of myths, ceremonies and folk tales with only an honorary leader. It has no set religious texts or clergy, and beliefs very greatly from one subscriber to another. Stition's believers can't truly be considered 'members'- however, as it competes with other organized religions and is poorly understood, it is often counted among them in religious scholarship. Recent scholarship is only now bringing Stition's origins and common beliefs to light, alowing the nobility to once again laugh haughtily behind the back of its adherents.
Halledammerung: an apocalyptic, polytheistic religion that incorporates many of the figures found in other religions into its own pantheon. Held in particular contempt by most other religions, it has often been banned for causing distress with its consistent predictions of upheaval and chaos.