It is formed of a core set of rules for any genre, and then a number of extensions which are for specific game worlds. There are literally hundreds of such systems available on the web so here are a few things that we think make it unusual (I would not like to go so far as to say unique because I’ve not reviewed all the other games so cannot prove it
• The combat system is continuous with no rounds, people can act if they are ready to do so, which makes it fast paced and ensures everyone is always involved at all times (section 8 of the core Nucleus rulebook)
• Highly visual to hit system, that is quick and easy to resolve and works the same way for all types of attack (spells, grappling, vehicle combat, ranged and melee etc.), see section 9 of the core rulebook
• Generic power /spell system, it is simple intuitive and allows castors considerable flexibility in how they expend their power, it been used in situations as diverse as magic, alchemy and psonics. See section 21 of the core rulebook
Features you would expect are also present
• Extendable, it has been designed to be extendable into any game world I(this is not unique at all, but important we feel)
• Realistic, obviously it can never be perfect but we have done our best to make it as realistic as possible
• Simple, once up to speed with the rules you rarely need the rulebook, almost all the tables are calculated from simple formulas which are all you have to remember
• Easy and unlimited skill progression, skills have no caps, experience and development is based on a point based classless system, see section 19 of the core rulebook, and character creation in section 2
• Generic weapon rules, no need for large weapon tables, all weapon stats are derived from simple formulas, special weapons are variations on these, see section 13 of the core rulebook for an example
• Its free, and in constant development