The Cortex system is an RPG system where die-size represents skill or potency. For instance, a Stealth skill of d6 would be worse than an Alertness of d12. Use this tag by itself to denote something common to other cortex games or with a specific game tag to provide the necessary context to your question.
The Cortex system is used in all of the RPGs for licensed properties produced by Margaret Weis Productions.
The bones of the Cortex system were first seen (but not named) in the Sovereign Stone RPG.
The system was evolved again for use in the battlestar-galactica RPG, which may be where the Cortex Plus designation originated.
In-print games using the system include the leverage RPG, the Smallville RPG, the Supernatural RPG, and the Marvel Heroic RPG.
Leverage and Smallville use modified versions of the system called Cortex Plus Action and Cortex Plus Drama, respectively. marvel-heroic uses a modified version called Cortex Plus. The cortex-plus tag should be used for these systems.