Creatures are summoned in ACKS by spells or rituals (depending on how powerful the creature is). Right now, from what I understand, this is what you can do with a summoned creature:
Use it in immediate combat (if casting time is short enough).
Use it as a temporary “henchman” (for spells with longer duration, e.g. Summon Efreeti.
Use a creature’s power (e.g. an Efreeti’s Create Permanent Goods).
Use a creature’s one-time unique power (e.g. an Efreeti’s Wish).
But in the spirit of Sword & sorcery, i.e. vile sorcerers summoning demons for various nefarious ends, I was thinking about allowing the following in addition to the above:
Assist with magical research, at least when summoning is for a longer period (e.g. an Efreeti’s 33 1/3 days). Maybe grant a +1 (+2? +4?) bonus to a spell research throw when a powerful (HD10+?) extraplanar creature assists in the research.
Replace Special Components in magical items and similar creations. Instead of, for example, using the ichor of 4 Efreeti to create an item, you’ll be able to summon 4 Efreeti who will work on the item using their unique daemonic skills and craftmanship.
Use in D@W war. I’d like to be able to summon an Avatar of K’tulu big enough to serve as a military unit on his own! Just imagine the terror of a castle’s defenders when this tentacled giant marches at it!
Provide a spell/construct/etc formula. Probably as a singular service, which releases the creature of any further duties.
I think some of those sound like unique campaign specific spells or lootable scrolls, but in general anything where summoning outsiders for power and enhanced magical learning is at least thematically incredibly appropriate. If you summon a creature naturally gifted with deeply powerful innate magic like an a djinn or efreet then I’d like to think they would have some colorful commentary on how much work the mortal caster is putting into relatively “childish magics.”
For assisting in magical research, I would judge how risky it is, then give you a bonus based on comparing it to experimentation.
For example, if there’s barely any risk at all (cast the spell and get the bonus), I would not give you more than a +1 bonus. If the creature might break free and try to kill you, that’s a +2. If the creature will definitely come back to hunt you down afterwards, that’s a +4. If the creature is a Lord of the City of Brass and will come back with an army of fire elementals to hunt you down and burn every place your footsteps have ever fallen, that’s a +6. (Ok, maybe that’s a +8, since radical experimentation doesn’t fail every time. But you get the point.)
I would recommend against allowing number 2 (serving as special components), unless there is a significant risk involved. I wouldn’t want to let wizards turn spell slots into special components; that seems to me that it would just make magic item construction require a repertoire tax instead of the special components, because what wizard would rather hunt down 200 ogre skulls than cast some spells? Perhaps they could change the special component required; that is, summoning demons might allow you to use ‘souls’ as a generic component similar to divine power, but you would still need to earn the component.
3 (serve as a D@W unit) is easy, you just have to summon something big enough that it matters. Summon Dragon already does this, and indeed is mentioned in D@W. For any creature that isn’t already in D@W (which is to say, homebrewed monsters), you’d simply have to figure out their unit stats and then you’d be good to go.
4 (provide a formula) seems pretty neat. You’d summon specific types of creatures for specific types of formulas or items; I’d only allow an efreet to know fire-related formulas, for example. If you want a carpet of flying, you go to a djinn, but if you want a wand of fireballs, you go to the efreet. In order to minimize the amount that this warps the campaign world, I recommend giving their formulas annoying special components. As an example of what I mean, it’s a lot easier to gather a whole pile of goblin hearts than it is to gather the fingerbones of an archmage, even though both might have the same GP value. I would lean the formulas known by summoned creatures towards the ‘fingerbones of an archmage’ end.