It was part of one of the Kickstarter previews.
Basically it gave access to a few specific low level ranks of summons with a rating between 1 and 4. The summoner can have up to their Summoning score in those summons. There was an enhanced set of rules for named beings where a deal was struck.
Converting it to Dresden it would be
Ritual-Summoning.
You could summon up to your conviction score worth of total summons. They can be any element.
Sponsored Magic-Your Element Here-Summoning. -1
Now, in fatecore refresh amounts are much smaller, all a summoner needs to do is take the appropriate spell instead of taking ritual. This is less appropriate for Dresden where there are pre-existing "Caster Skills"
I'm unsure if posting the abilities of each level of summon are appropriate here, as they are not yet open to the general public and you missed the kickstarter(I think.)
Actually, I was looking over the Refresh Values of the stuff in Fate Core, and realized that the refresh ratings give you the ONE element/ritual without the item slots (basically, sans Refinement), so the numbers actually make sense.
The summoning rules basically dictate that the highest skill the summoned being has was your difficulty to summon the entity if I remember correctly. It, of course, did not factor in powers and whatnot, and makes the summoning of a "weak" creature very easy, which could work for Binder's goons (as they were one-shotted with maybe a skill rating of +1 or even +2, relying on sheer numbers to succeed).
I have two problems with these rules: the first is that it can make it very easy to summon a one-trick pony, but it also makes said one-trick pony a viable tool for a short period of time. The second makes it difficult to scale a more powerful entity, as it doesn't include the powers loadout.
Perhaps the difficulty for a short-term summoning should be Highest Skill + Refresh of Powers? While it may not be as difficult as "taking out" the target, it does leave leeway for increased diffficulties for longer tracks of time, specific commands, etc.
One of the reasons I'm even considering this: I'm running a game at an anime convention, and one of the other GMs mentioned I should watch a few newer series, one of them being Fate/Zero. I'm now trying to determine how to get one of the Servants summoned to work within this game without making the servant a second PC.