I run a Demon Hunters game. The rules are based on a mix of Fate Core and FAE.
Basic checks are made with two dice, Approach + Discipline (plus certain optional dice which we can ignore for now). Unopposed checks have to beat a certain target level (5, 10, 15, ...) while opposed checks (including Attacks) have to beat whatever the opponent rolls. For Attacks, if the attacker rolls X and the defender Y, the latter takes Y-X Hits.
Now, one of the characters in my group uses pastry-nades. I don't quite know how do model these well. I could find nothing in the Fate or FAE rules, either. The issues I'm having apply to other AoE-style attacks; I'll stick to the grenade terminology.
Here are some options I can think of.
Perform a regular Attack action which against target in the AoE has to defend against separately.
Problem: Either the grenade hits as planned, or it doesn't. Why would every target "dodge" differently, and receive very different damage values? This does not seem to model the disconnect between the attacking action and the actual source of the damage well. Also, invoking Aspects for throwing better would translate into Hits, which is ... weird.
Then again, some Aspects could reasonably explain higher damage, such as cramped quarters.
Perform a skill check for throwing the grenade. Level depends on how difficult that throw is, and opponents can Defend if the narrative allows for it. When the grenade explodes -- whereever it is now -- everyone in the AoE has to Defend against a fixed level (which may depend on the grenade; I'm thinking 10 for basic stuff).
Problem: This is more complicated, and may become overpowered. Throwing a grenade would usually be easy (5-10, I guess) and damage output would only depend on the grenade thrown. I've seen (and used!) this in Shadowrun, and it can be quite problematic.
But then, the character could only invoke Aspects for the throw, not the actually damage which may put a cap on the power of grenades here -- which in turn could be problematic for a character whose concept revolves around this.
How would you model AoE attacks/effects in Fate- or FAE-based system? How do you avoid making grenades overpowered or obsolete?