I've been thinking about mechanics.
For example, tabletop games. Most tabletop games use a descendant of the wargame rule sets - turn-based combat-heavy rules. Even the ones which have simultaneous turns are usually still turn-based. I've talked about this in some detail before.
Rather than simply thinking about other kind of rules, it's worth thinking more about these time-tested paints we've all used a thousand times. The fundamental mechanics of nearly every tabletop game are the same, but they have very different feels depending on how things are weighted and, of course, the kind of world you've set it in. Ideally, the world and the rules should support each other perfectly.
Sometimes, a world is born out of a fascinating rule. But, more often the rules are built to support a fascinating world. And that's easiest to do when you are working within a scaffold: a painter does not invent a new paint for every canvas. Instead, they master painting and use whatever paints serve the work.
With that in mind, it's worth examining the various "paints" we might use to support worlds we have invented, stories we want the players to tell. I don't even think they have to be described in detail - if I did, they would require a post each. But we'll go over them briefly.
The battle rules are, in most cases, the heart of the game. There's actually a few paints hidden here.
One is the amount of time each battle takes, both in terms of turns, and in terms of how much real time the players spend per turn. Generally, battles with fewer turns tend to focus more on proven fundamentals, so characters in those games tend to have to choose between unlimited basic techniques and limited high-power techniques, and that's the fundamental point of combat. Battles with more turns tend to play more tactically, letting the players experiment and play with long-term effects. These basics are usually true even if you're using a miniatures map.
Of course, systems with battles that take more time tend to also focus more on battling. It may be that shorter battles are better simply because you want to spend more time on other things.
Battles can vary in terms of information inequality. Some systems, every decision you make is in full awareness of the outcome. Other systems, the players are desperately slogging through a statistical fog. This can be from things like simultaneous turns, but it can also be from simple randomness such as having to roll to hit.
Lethality matters, of course. Generally the players are always going to be quite lethal. The question is whether the enemies are going to be lethal. A lot of systems, the players are expected to win every battle pretty handily. These systems tend to have a lot of statistical fallbacks and make up for it by having epic boss battles. Other systems, every battle is a desperate struggle that could go badly for one or more players.
Another factor worth considering is how much your combat "mixes" with the rest of your game world. Some games pull stuff from the outside world into combat, allowing players to plan things out such as planting explosives, messing with the guard's communicators, using giant cranes to crush the dragon, etc.
However, in most situations it goes the other way. The consideration is how much attrition you put into each battle. Attrition is not simply how difficult it is to recover hit points, but also how many resources in general you must expend during a fight. If you have a "short battle" system your characters will typically expend a lot of limited-shot abilities. The reigning systems of the day don't much like attrition, so it's usually pretty easy to recover wasted abilities.
Moving steadily out of the path of battles, you run into the idea stats and stat progression.
The more complex your stat system is, the more meat the players have to chew on. More complicated stat systems are suitable for longer games with more experienced players, while simpler systems are more suited to pick-up games and newbies. Some people prefer simpler stats as a matter of preference, but I find they don't offer enough traction for longer games with experienced players.
Stat progression and customization is also critical. The two basic methods are equipment and level-ups. The more complicated and branching the options are for these, the more meat there is to chew. Generally, games match statistical complexity and augment complexity.
As we get further from battle again, we start to enter the noncombat mechanics. The biggest choice here is where the blending happens between rules and role play. For example, most games have social skills such as fast talk, intimidate, and so on. However, in practice the players role play social situations as much as possible before turning to a skill roll. Similarly, they may have stealth, or mapping, or so on, but in general most players appreciate the GM explaining what they see and letting them approach it from a role-play perspective instead of rolling for everything.
Some games mix it more freely, such as giving the players slightly nebulous advantages if they call on various traits. Some games create a more complex rule set and draw the line more crisply. It depends on the approach you're going for. Some games have a lot of skill stuff, especially if they are set in the future and have things like piloting, hacking, repair, market research, etc. Fantasy games tend to have noncombat situations that can be resolved primarily by role play. Creating a complex skill framework for a fantasy game can result in a really complex framework that ends up not mattering very much.
There are some other "paints", but they are more tightly integrated with world design. For example, can your heroes retreat safely from extended conflicts? Can they rest safely in the wilderness and recover their spent energy? Can they rely on magical solutions, help from strong authority figures, and so on?
These decisions sound more like world design than rule design, but in truth the boundary is pretty blurry. If you can convince a god to come down and handle the dragon, then that's going to effect your battle plans as much as if you have to expend resources every time you fight.
Anyway, I think that's most of the paints you might use. If you have any thoughts, I'm interested to hear them.