[6]: 353  Chambers designed Serenity Role Playing Game (2005) using the Cortex System, the first release from Margaret Weis Productions.

[6]: 353 Through Margaret Weis Productions, Chambers also created and published the role playing games Battlestar Galactica and Supernatural.

At the time, Serenity RPG was the most popular role playing game since the original Dungeons and Dragons, requiring four print runs in the first year of publishing.

[7] Chambers created the Cortex System for the Serenity Role Playing Game during his time at Margaret Weis Productions.

He then used it for additional licensed game supplements, several of which were based on television shows and movies, including Battlestar Galactica and Supernatural.