Klaus said:No AC, just Defenses (re-named Saving Throws), which are static.
Everyone has a Standard, Move and Swift action per round. You can trade an action for a lesser one, and several actions require that you spend more actions in a round (aiming, for instance, requires two swift actions, so you'll stand still while aiming, and then ignore less-than-total cover).
Condition Monitor (Normal, -1, -2, -5, -10, unconscious or disabled).
Objects are subject to critical hits and have a condition monitor as well.
Every natural 20 is a hit, and is a critical (no confirmation roll needed).
No iteractive attacks (+11/+6/+1). You can take feats to attack more than once in a round, but all attacks are at the same penalty (attack once at +14 or twice at +9/+9).
Class-based bonus to defenses. If you multiclass, use the best bonus (and they're flat).
Level-based bonus to defenses. If you wear armor, you *must* use the armor's bonus instead. You can take talents that allow you to choose wether to use your level- or armor-based bonus, and later on you can use both.
Etc, etc...
From this list I believe the ones you can't find in other books are Condition Monitor and the swift-action trading system. Not entirely sure though.