OK, you all know my base system - StarCluster - is a framework system. It can accept most any bolt-on sub-system so long as the interface is correct. What the system cares about is fairly limited - its 'interface'. It has certain values it presents to the subsystem - these are the system's 'tools'. It expects certain values in return. So long as the system gets these values in the proper range or ratio, it doesn't care how they got there. Let's examine the Resolution sub-system.
The system's tools are Attributes, Skills, and Modifiers. Attributes can range from 1 to 15, though this is a limitation only because of certain sub-systems - StarPerc, for example, can work with arbitrarily high Attribute values, while StarPool needs a limitation to work - in order to keep the interface compatible, the limits are necessary. Skills are ranked, with +0 being unskilled, +1 being skilled, +3 being expert, and +5 being master. They can range arbitrarily highly, with multiples of +5 being Levels of Mastery. Modifiers are presented in two classes - Small and Large. You can add modifiers together - i.e. 2 Small or 1 Small and 1 Large - but they are not necessarily on the same scale. in StarPool, for example, a Small modifier is worth + or - one to a Target Number, where a Large Modifier is worth + or - one die.
There is a derived stat - Constitution - which represents the pool of physical damage the character can take. This is always expressed as the four physical attributes added together and multiplied by some value. That value varies from sub-system to sub-system, and may vary within a single sub-system.
The most basic value the system needs in return is whether or not the attempt was successful - the Chance of Success. This is binary - yes or no, zero or one - however you want to phrase it. This can be generated by whatever means are needed - it's not a complex problem. I try to set a typical skilled person to have a success at around 45-50% of the time.
The second value returned is Quality of Success. Physical combat damage is an example of Quality of Success, and is expressed in play as Quality of Success + Weapon Damage Modifier. WDM is a value - positive or negative - which is added to the base QoS. How the QoS is generated depends on the sub-system. In StarPerc, a separate d% roll is made, while in StarPool, successes are counted and multiplied times 10. This number needs to be in balance with the Constitution for the feel you want. In a gritty game, you probably want a single hit to potentially kill. In a more cinematic game, you may want a danger of death only after several hits. You may not want death at all in - for example - a supers game, so you would substitute some other penalty. Working out the proper balance of damage and Constitution is a huge part of establishing the feel. In StarPerc, Chance of Success varies greatly by skill, and Quality is extra-ordinarily random, while in Star Pool, skill affects both Chance and Quality.
Other things, like Traits and Edges, are expressed as modifiers. Each rank of Trait or Edge is worth a Small Modifier, with the differences coming in other ways - Traits are a limited, refreshable resource, while Edges are more dependent on situation and condition.
So let's take the StarNova sub-system and see how it works within the StarCluster framework:
A Skill Check is made by rolling d6s and adding them, with any 6 exploding - i.e. generating another die to roll. Skill controls the number of dice rolled - 1 die per skill rank, plus 1 die. The extra die being to account for unskilled attempts.
Attributes give a bonus for high attributes and penalties for low attributes. This is +1 per 2 over seven - at 9 (+1), 11 (+2), 13 (+3), and 15(+4). This bonus is added to the roll.
A Success is made - i.e. Chance of Success - when the total exceeds 9. This is *just* possible Unskilled if a 6 is rolled. A Skilled character rolls 2 dice, and may succeed without an attribute bonus or an exploding 6. A Master rolls six dice, so even a mix of ones and twos can succeed.
The Quality of Success is the total number rolled. This will usually be a fairly low number of at least 9, but with no cap. Constitution should also be fairly low. I wanted a gritty feel, so I chose 2 as the Constitution Multiplier. Weapon damage bonus can be quite high, so better weapons are definitely much deadlier. Average human Constitution will be around 60, while WDM can be up to +50. If you want a less gritty feel, the easiest thing to change is the Constitution Multiplier. A CM of 4 would bring average human Constitution up to 120 - much more survivable!
Initiative is arbitrary really. I do keep Initiative on the same level as chance of success, so that you can trade one for the other on the same scale, as an abstract tactic. I put Initiative at 1d6, highest goes first, with each point of init traded being worth +1 to the roll total.
So, there is how the interface works. The means of generation and resolution may vary, but the character doesn't.