What system was developed by Margaret Weis Productions was used in a game based on the Supernatural TV series?
Cortex System: The Cortex System is a generic RPG system based on the "Sovereign Stone System ", and was developed by Margaret Weis Productions, Ltd for the Serenity Role Playing Game. Supernatural Role Playing Game: The Supernatural Role Playing Game is a role-playing game by Margaret Weis Productions that was released in 2009. Supernatural Role Playing Game:  It is based on the television series "Supernatural" and was the final game to use the Cortex System.
The Cortex System