Dissonance is a magic system more than a setting, and can be applied to any worlds. Here is its description as it applied to Earth.

Description
The magic has Principles. These Principles can be set to other things via a complex ritual involving a lot of magic and users of all of them. The last time this was successfully accomplished was in the Middle Ages, and the people who set it up set the seven heavenly virtues as the Principles: chastity, charity, humility, kindness, temperance, patience, and diligence. Their opposites, then, are lust, greed, pride, envy, gluttony, wrath, and sloth.

When you act in accordance with the Principles, you start storing harmonic magic. When you act contrary to them (in accordance with their opposites), you gain dissonant magic. It is possible to have stores of both by acting in accordance with some Principles and contrary to others, but if you act in accordance with a Principle and then act against it (or vice-versa) you lose the magic you gained in the first place, so most people have approximately no magic stored, on average. Moreover, even the people that do have magic have a real hard time noticing it. It's like Tom Cruise's middle tooth: most people will never realise he has a middle tooth until they are told, and then they will never be able to fail to notice it, but some people notice the tooth all on their own. It is of course much harder to notice than that, so the vast majority of people just won't notice it. After noticing it, though, you'll be able to direct your actions to be more effective at gathering magic, and you'll be able to know when other places/people are using this magic or have had it used on them.

The stores of magic are fuzzy and not really numeric; they work more like the magic owing you favours than like some quantity you spend to do stuff. If you are very harmonious/dissonant, you can pull off bigger things, and that does deplete some of your magic store but not in an altogether fixed and easily measurable way. If the magic "trusts" you particularly, you can even pull off stuff that's way bigger than what you'd strictly be able to do, but if you do that and then stop acting relevantly harmoniously/dissonantly then magic feels cheated and you'll have a hard time rebuilding your magic later.

The kinds of effects you can achieve are more based on the #aesthetic than a specific list of things. There are some things you can achieve via both harmonious and dissonant magic, and some things only one of those can do. As an example, suppose you have a bouquet of 100 red flowers and 1 blue flower. You can easily use harmonic magic to turn the blue flower red to fit its surroundings, or a bit less easily use harmonic magic to turn the red flowers blue. You can't turn them altogether different colours, though. If you use dissonant magic, however, you can in fact turn the bouquet into a rainbow of colours, or turn them blue-and-red, but you can't ever turn all of them a single colour - although if you're clever you can turn all but one of them blue. The relevant #aesthetic for harmonic magic is enhancement, improvement, equality, coherence, reinforcement, maintenance; the relevant #aesthetic for dissonant magic is change, breakage, chaos, decoherence, contradiction. There is probably something akin to "moving your pain from left to right" associated with using/noticing the magic but if so it is as-of-yet undecided.

Magic is secret, and it's mostly only the elite of the elite keeping it, the rich and famous who apply it to secure their success. It's easier to apply magic to processes than to end results - in other words, making sure a cake you're baking comes out delicious is easier than getting a cake and then trying to make it tastier - and the families that know of magic often apply it on themselves and their children as they grow up, making it more likely for them to turn out pretty, smart, athletic, sociable, etc. It's also easier to apply magic if you're more specific about what it's affecting and if you know more about your target - a doctor would have an easier time using magic to kill a disease because they can target better, it's easier to do magic to objects than people because objects are simpler, it's easier to do magic to yourself than others because you know yourself better.

Counter-principles and Principles

• Lust (vs. Chastity): Lust is about temptation, it's about looking at something that you really want to do and just doing it, and you get bonus points if it's inadvisable or other considerations would make you normally reconsider or think twice before making this choice. Chastity is then about resisting this, about heeding your conscience and your better nature.


• Gluttony (vs. Temperance): Gluttony is about excess, it's about having more than you need and getting even more, it's about hedonism and limitlessness and your own pleasure regardless of consequences. Temperance is, appropriately enough, about not doing that, about having what's wise and reasonable, even though you could get more, one more slice of cake, one more hour playing video games, one more, it's about having just enough, just what you need, not anything more.


• Greed (vs. Charity): Greed is about not sharing, it's about having more than other people and not giving what you have extra, it's about hoarding and accumulating and keeping, it's about having more money, more status, more fame, even though you're not gonna use that, just because you can have more and other people can't. Charity is then about sharing what you do have, donating your money, your time, your attention, it's giving others that which, to you, is superfluous.


• Sloth (vs. Diligence): Sloth is about doing the bare minimum, it's about something that has to be done and doing the least amount of work needed, cutting corners, genuinely risking not getting the thing done because you didn't put in as much effort as you could (higher the risk, higher the reward). Diligence is about putting the effort and work in, about figuring out how to do what you want to do correctly and completely. Note that efficiency is not laziness - if you put in the work to figure out what the most efficient way to get the thing you want done is, and do that, that's not lazy; it would be lazy to not care and do whatever seems easiest.


• Pride (vs. Humility): Pride is about status and image and self-trust, it's about doing things that will make people think better of you and it's about trusting yourself more than other people, it's about hubris and listening to your own wisdom above that of others. Humility is about deferring to the majority, about being meek and unassuming, about not standing out and not doing things that will bring attention to you, about trusting other people's judgment above your own.


• Wrath (vs. Patience): Wrath is about lack of self-control, it's about not dealing with other people's bullshit and about righteous fury, it's about doing things in the passion of the moment with the blood still hot. Patience is about being cool, about not letting your emotions control you, about restraint and calculation and being understanding and, well, patient.


• Envy (vs. Kindness) : Envy is about seeking out what others have because they have it, it's about tearing other people down for your own gain, stealing their glory, using other people's work as your own, winning at the expense of others, copying them and refusing to help them. Kindness is about selflessness, it's about realising the importance of everyone else and acting on it, about making sure others shine as much as they deserve to and seeking to prop them up rather than tear them down.

Details

• After you've first noticed magic it is possible to detect it in oneself, others, and the environment, like an extra sense specific for it.


• If you're working on a Principle/Counter-Principle X and then you do not-X, you lose more magic than you would've gained if you'd been working on not-X. That, plus the fact that most actions aligned with a principle are not sufficiently that-principle to get you much magic anyway (you'd have to be the equivalent of the school slut in a given Principle/Counter-Principle to reliably get magic from it) is the reason why most people have zero net magic.


• Doing magic in a way that's aligned with a Principle/Counter-Principle is easier/"costs less" than not doing that. So, for instance, using kindness magic to dry someone else's clothes after they get out of the rain is more efficient than just drying your own clothes.