Editing Unwritten: System Reference Document/Aspects and Fate Points (section)

===Free Invocations===

You don’t always have to pay a fate point to invoke an aspect—sometimes it’s free.

When you succeed at creating an advantage, you “stick” a free invocation onto an aspect. If you excel on the action, you get two invocations. Some of the other actions also give you free boosts. You also get to stick a free invocation on any consequences you inflict in a conflict.

Free invocations work like normal ones except in two ways: no fate points are exchanged, and you can stack them with a normal invocation for a better bonus. So you can use a free invocation and pay a fate point on the same aspect to get a +4 bonus instead of a +2, two rerolls instead of one, or you can add +4 to another character’s roll or increase passive opposition by +4. Or you could split the benefits, getting a reroll and a +2 bonus. You can also stack multiple free invocations together.

After you’ve used your free invocation, if the aspect in question is still around, you can keep invoking it by spending fate points.

If you want, you can pass your free invocation to another character. That allows you to get some teamwork going between you and a buddy. This is really useful in a conflict if you want to set someone up for a big finish—have everyone create an advantage and pass their free invocations onto one person, then that person stacks all of them up at once for a huge bonus.