Mostly I’ve been curious about their statistics and whatnot, since I have the half-baked idea to switch dice mechanics depending on scene/setting or something for the Starblazer game I’m building: a more cinematic world uses d6-d6, while a space hulk horror session uses 4dF because it’s weighted towards zero.
The main thing to keep in mind: FATE, and Fudge, are systems based on “margin of success.” Having a Good skill means, most like, you’ll succeed on a Fair task/challenge; hence the dice systems pushing a bell curve aiming at zero. You still need to over-succeed to the point where you don’t just succeed with a Fair result, but generate some spin to do extra damage or decrease the time spent/increase quality. That’s changed a bit since Spirit of the Century came out—at least, in that other publishers are moving a little away from the idea with more “extreme results” mechanics.
4dF: Using Fudge dice goes back to the Fudge system, Fate’s progenitor, but there is a lot going for them. (A lot of people swear by them for all Fate games, at least.) The idea is to generate a total between +4 and -4, with a bell curve aiming straight at 0; to get there you roll four d6’s, each one having two “+” sides, two blank sides, and two “-” sides, then adding the results together. (If you’re a fan of math, you can do this at home with normal d6’s by rolling high/medium/low and factoring as +/blank/-.)
Because it’s a dice pool, things work very well towards creating the desired bell curve around zero: it’s unlikely you’ll roll many -4 or +4 rolls. In fact, the majority of your rolls will be within one step of zero, giving a lot of +1 and -1 results. That’s what Fate originally wanted, putting an emphasis on your skills and less on blind chance, though making things chancy for those low-ranked Average skills.
1d6-1d6: This was introduced with Starblazer Adventures, and goes in the opposite direction. You’re rolling two dice, one generating a positive number and the other generating a negative number, and adding them together. Here, you have two independent variables doing multiple things: you want one to roll low, and another to roll high. And you have to do the dreaded maths.
Unlike Fudge dice, this system is pure chaos; while (statistically) the bell curve is still around zero, with a lot of 1 and 2 results, things are expanded a bit in both directions. You’re a lot more likely to roll an extreme result; while those fives aren’t going to show up that often, the chances of rolling a three or four (+ or -) is a lot more likely than with Fudge dice.
Thus, it’s a tradeoff: less certainty of results around zero, but a lot of chaos and the chance for a big +5 payoff. 4dF is somewhat predictable and safe in its bell curve. d6-d6 theoretically has the same bell curve, but with higher end variables, leading to high risk, high reward. More importantly, it’s the system to use if the FATE game in question rewards shifts (successes by three or more).
(I have to admit, this is the one I’m leaning towards liking the most; its extreme results fit best with pulp and space opera in my mind. I recommend using light and dark dice to keep the numbers separated, or go with negative pips and positive numbers or something.)
2d6-7: Another option, to keep things simple: roll two d6’s, sum them, and subtract seven. You’re still ending up with the same -5 to +5 variable as with d6-d6, giving you the chance for major success or critical failure, but is a much more traditional formula. It’s a lot easier for newer players than rolling high-med-low or remember which is the negative die.
4dF is a predictable dice pool; d6-d6 is pure fate. This style is somewhere in between, and follows traditional RPG dice mechanics of “high is good, low is bad.” However, it falls back into predictability: you need both of your dice to roll high consistently, otherwise you’re boned. One system’s +5 and -2 would be a nice solid +3, but here, it’s a flat zero. (Of course, flip the modifiers around and you have a -3; those modifiers are something you just can’t control in d6-d6.)
It lacks the stability of 4dF and the random chance of d6-d6; on the other hand, it’s simple, straightforward, and lacks the random chance of d6-d6, putting it closer in stable predictability to 4dF.
3dF/5dF: There’s been some discussion about the benefits of using more/less Fudge dice. Either way disrupts the 4dF zero-based bell curve, but both have results more along the lines of 4dF’s predictability than some of the more random dice systems.
2d6, take lowest number and add die +/- modifier: Here’s one I saw posted on forums a while ago that some gamers are now using. Roll two d6, a negative and positive die (in some cases, 4d6, two positive and two negative); then, take the lowest numerical roll, and apply the modifier (+/-) of the die it’s on. Sixes (or tied sixes, I forgot) are treated as zero. Thus a roll of +3 and -1 would take the lowest numerical value (the one) and apply its dice modifier (negative) as the end result. By contrast, +2 and -6 would have an end result of +2.
It’s an interesting system, but I’m not sure I’d use it. It’s even more chaotic than d6-d6, which is hilariously chaotic to start with, while cutting out its random chance for extreme results. It’s chaos, but a systematic, streamlined one that minimizes the chances for huge success or failure. Most of the problem would be selling players on a system that has its own learning curve.
There’s always the option to use Technoir dice, which is a fascinating (if complex) system of spending Fate points as additional dice. Something like ICONS’ use of Determination to succeed at a task plus archetypical stunt/edge/action dice. Again, I like it for its games theory aspect, but when my prospective players are new to FATE (and me) I’d rather stick with something simple for them.
And there’s a system for making FATE rolls with a tarot deck.
One final note: I’m curious as to how 4dF works with ICONS. Most FATE characters have a skill pyramid with a single +5 or +4, while most starting ICONS characters rarely have attributes ranked lower than 3-4. 4dF is the closest of all these systems to having a pure bell curve of zero, so my assumption is ICONS characters would succeed constantly with 4dF, hence why the raw chaos of d6-d6 was used.