First a Power is defined (GURPS Powers, p. 7) as A “power” is an exotic or supernatural gift that you can direct in different ways to produce a number of related effects. Further it goes on to say that it must have a source (Magic, psi, mutant, etc) which is the origin or where it comes from and a focus (fire, water, matter manipulation) which is what it manipulates or controls or the concept it revolves around. This is the special effect or narrative description of a power which also has a mechanical description (how you build it in GURPS) which consists of Abilities, Power Modifier, and Power Talent.
Power frameworks are simply a mechanical way to group related abilities so that they are cheaper because they are related, much as skill defaults can be used to buy related skills more cheaply.
- The Power Modifier (PM) is the basic starting point in that all the powers have it and can be countered in the same manner (such as with the Static advantage).
- Alternative Abilities introduced in GURPS Basic as Alternative Attack and later expanded upon in GURPS Powers and Power-Ups 8: Limitations allows you to buy other abilities of the same power at 1/5 cost. To get the discount they have to be no more expensive than the primary ability, they are all neutralized together, only one is available at any specific time - usually takes a Ready maneuver to swap them around. It gets a little fancier, read Power-ups 8 for more options. GURPS Powers: Divine Favor, GURPS Powers: Totem and Nature Spirits, and GURPS Thaumatology: Sorcery are all worked examples of this framework.
- Wildcard Powers (GURPS Supers, p. 41) allow you to have a variable secondary ability while using the ability modified this way. Your paying *4 cost for the privilege of having two abilities at once. This may not seem like a good deal at first since you could buy 4 powers for the same price but for broad powers with many options and uses it can be an effective and simple tool.
- Originally Posted by whswhs (SJG Forums)
And that's how wildcard powers should be used, too. They open the door to freeform improvisation, but you have to tie them to a use of the underlying power. But that freeform style of play is meant to be there. If that's not what you want—if you want to spell out what you can and can't do—you shouldn't take a wildcard power in the first place.
- I think the above quote is a real good case for when these are at their best.
- Modular Abilities is an advantage that costs a premium in order that the player can swap various related abilities around. Its written up as an advantage but in practice its really a power framework. GURPS Thaumatology: Sorcery combines this with alternative abilities to increase point efficiency.
- Power Stunts (GURPS Powers, pp. 170-178) is another way to handle multiple abilities of the same power. There are a lot of options here and the utility of this section really escaped me until I read GURPS Psionic Powers which is pretty much built around this section of GURPS Powers. Using Abilities at Default takes a specific ability and swap it for another one with a successful HT/Will or skill roll and paying 3 FP and you can have a variety of abilities for very little cost. Even putting a lot of points into a skill to easily make the rolls (which can have up to -10 in penalties) or Techniques for specific swaps (as done in GURPS Psionic Powers) this can still be cheaper than alternative abilities, though that FP cost can hurt - especially in combat. This section also includes Temporary Enhancements which instead of swapping out one ability for another increases its power or adds enhancements by making a similar roll as Using Abilities at Default but only costs 2 FP. Finally Extra Effort (Powers, pp. which allows boosting the level of a power (capped at +100% - but see Godlike Extra Effort)) by making a roll at a penalty of -1 per +5% and paying 1 FP. GURPS Psionic Powers is the best and most detailed worked example of this type of framework, though GURPS Thaumatology: Chinese Elemental Magic and GURPS Powers: Totem and Nature Spirits also touch on it.
- GURPS Power-ups 1: Imbuements could be considered another framework. You have a core power costing 10, 20, or 40 points and skills to do various things. If you really look at it its uses something like Power Stunts to enhance mundane weapon or skill use but uses a VH skill for each basic ability with penalties to add enhancements and costs 1 FP. A key difference here is that you can have multiple abilities at the same time. In this sense its more like GURPS Magic.
- The exact math never quite made perfects sense to me, I think mostly because with no core ability bought with points it uses a lot of author judgement. Christopher Rice attempts to explain it here in GURPS 101: Designing New Imbuements.
- In questioning him he replied "I suppose I should have been more specific - you only need a single level. So Deafening Display is Obscure Hearing 1  compared to the "average" cost of damage of 7. So 2/7 = 0.28... or around 30%" So the example of Deafening Display requires Imbue 1 since its a 30% effect. Much clearer to me.
Taken together GURPS has quite a few ways to build effective powers based characters, each with their own trade-offs. The primary differences being between point cost, FP cost, time to swap, and skill rolls that may be required.
Another Supers game that I played called Champions (2nd edition I think) had three specific power frameworks. Variable Power Pools (Modular Abilities), Multipowers (Alternative abilities) and Elemental Controls (no match in GURPS, though Wildcard Powers is the most similar).
In my personal opinion GURPS Fourth Edition is not only the best incarnation of GURPS it makes the best powers based gaming which is great for Supers campaigns. I have played Villains & Vigilantes, Champions, Marvel Super Heroes, Heroes Unlimited, and read a few others. Champions is my second favorite and a little simpler to play and build characters with but it felt a little shallow to me and I could not build everything from the comics in it which I can do with GURPS.