Spirit of the Century had a lot of stunts. And that's awesome, I still use it as a reference manual for what kinds of stunts to give characters in other FATE games. I think that's what stunts should be: a long list of crunchy bits that can't be modeled by the other rules. Feats are my favorite part of 3.5/Pathfinder, and to a certain type of gamer pouring through multiple books for just the right combination of abilities is half the fun. But not everyone has that kind of fun, and so were born the SotC stuntless rules. They distilled the essence of stunts down to a few specific types, and gave you a way to access those effects via aspects.
Later versions of FATE, including FATE Core, seem to have met the stuntless rules halfway. Instead of 200+ pages of stunts, they've distilled stunts down to a few specific types and examples, and then encouraged you to make up your own. I understand why they did this. It succeeds nicely on keeping the page count down and the books affordable. Still, it's left me a little unsatisfied. Since I got my fun by pouring through those lists, being told to "make 'em up" takes a little of the fun out of them. And it leaves out the really interesting part of the actual stuntless rules, Dramatic Invocations. If you're gonna go that way, I say, go all the way and eliminate stunts.
One of Apocalithic's design goals is to be playable within it's own setting, so a big tome with a long list of stunts is pretty much out. For my own project I'm therefore adapting the stuntless rules to FATE core. And the good news is that's really simple. In essence we're simply going to append the rules about what stunts can do onto the rules for what invocations can do.
Take a look at page 91 of the kickstarter preview. Stunts are defined as being able to do three things: either add a new use to a skill, give a 2 shift bonus under certain circumstances, or simply break a rule.
In the second one we can immediately see the link to invocations, because that 2 shift bonus is what you get for a Fate Point. Adding a new use to a skill is pretty strait-forward. However, while "create a rules exception" is fair as a one time character creation thing, having to make snap judgments about what's a fair exception during play isn't viable. So we'll have to break that one down with a little help from the old stuntless rules.
Looking at the stuntless rules, several of them are made obsolete by the general "Declare a story detail" rule. However, I personally dislike the general nature of that rule and prefer that players have an aspect in order to use it.
In the end, the list of what you can do with an invocation on page 71 expands to the following:
• Take a +2 on your current skill roll.
• Reroll all your dice.
• Force someone to make a Fair (+2) overcome roll to deal with an obstacle represented by the aspect. If you do this before your target’s turn in a conflict, they have to use their turn on this action.
• Add a new use to a skill. This can either mean substituting one skill for another in a check, or using the skill in an entirely novel way.
• Provide active opposition when you otherwise couldn't. This might mean you get to defend when surprised, or roll notice even when not actively searching your environment, or use active opposition for things you made but are currently unattended using your craft skill, or anything else you can justify.
• Act Fast. Spend a Fate point to act immediately regardless of turn order in a conflict.
• Declare a story detail, as on p. 18 of the kickstarter preview. This can be introducing an NPC, having your special item on hand, or just know something important.
Now some players may want to force the last 4 to be used only on personal aspects. This is the default assumption for the SotC stuntless rules. But I prefer to allow these sorts of invocations on scene aspects as well, because it provides some interesting game play. For example, if the warehouse is Dark and shadowy someone could invoke that to defend against a ranged attack with stealth instead of athletics. Or someone Grappling someone else could invoke that in order to actively defend against anything the target does with their Physique. Taking this route clears up a lot of the edge cases about aspects and opposition that sometimes come up. However, if you aren't comfortable with letting every aspect be used this way, then section off some or all of the new invocation types and call them Dramatic Invocations. These invocations can only be made on your personal aspects, the ones on your character sheet.
Locking in an Aspect
Sometimes you just don't want to spend a Fate point every time your aspect comes up. The nature of what you are modelling is such that it should be involved every time, whether you've got a Fate point to spend or not. In these cases you want to Lock In the aspect. Pick one potential invocation of that aspect, then spend a point of Refresh. You get to invoke that aspect in that way for free, but you cannot invoke that aspect for any other purpose at all. A locked-in aspect is still subject to compels, and you still get the Fate point when it's compelled.
For example, you might have the Paranoid aspect. You decide to lower your refresh by one to lock it in. You chose to always provide active opposition with Notice when other people are sneaking up on you, justifying it by stating your paranoia causes you to constantly scan your surroundings for threats. Having locked it in, you'll always provide active opposition in this case, but you won't be able to use your paranoia in any other fashion.
A locked-in aspect is essentially equivalent to a stunt under the normal rules, but with the additional cost of an aspect. I like to think of it as trading versatility for consistency on your aspects.
Stuntless Rules and Extras.
When using these rules, Extras require a little extra thought. All extras will be aspects under this system. Essentially, an extra is a specifically defined list of viable invocations for that aspect. You spend a Fate point to invoke one of the possible uses listed on the extra. This where we get to pick up some of the more esoteric stunt uses again. Because an extra has to be pre-defined, you can add rules exceptions to how they work that simply aren't viable as on-the-fly invokes.
Extras also might require more than one point of refresh to lock in. If the extra provides more than one unique way of being invoked, then you have to spend a point of refresh for each unique invocation to lock it in. It may be possible to lock in only some aspects of the extra, leaving others open to standard invocation. Or you may have to lock in all potential invocations.
For example, Zird's "Collegia Arcana" extra (page 313 revised extras chapter) would be an aspect, but each use of Lore for magic would cost him a FATE point! Knowing that will get expensive fast, Zird locks in this aspect. Given that all it does is give new uses to an existing skill, his GM rules that as a single invocation type and charges one point of refresh to lock it in.
Meanwhile, the Super strength extra (page 316 revised extras chapter) has two possible invocations. You could just leave this as an aspect and invoke it normally, but it's hardly worth being an extra just for that. Instead you have the option of spending up to three points of refresh to lock it in for a fixed +2, +4, or +6 to physique checks. The Weapon (2) invocation is probably a separate thing, and can either be left alone to be invoked, or locked in with additional points of refresh.