User summary: The Nucleus Roleplay System is the primary rules book for the Nucleus Modifiable Game System (both titles are used apparently interchangeably). The system is designed to be a generic, universal rules system that is utilized with genre supplements to establish a campaign. Characters in the system have Basic Attributes (Agility, Deftness, Endurance, Intelligence, Might, Perception, and Presence). Attributes have Values ranging from -30 to 30, with an "average" person having a zero score. Attribute Values are purchased from a Proficiency Points pool. A number of Derived Attributes are calculated from Basic Attributes, most of them relating to combat. Characters have a Derived Attribute called Overall Life Points which are analogous to hit points in other systems. Characters also have Traits (negative and positive). Most opposed actions and combat elements use either a modified percentile roll (D100) or a type of action table that determines how many and which type of dice to roll.