Rigkit

Every rig RigKit builds is live. Nothing is baked into keyframes unless you ask for it. When you build a rig, the script reads your layer's geometry once to decide how many pieces to make, then writes expressions that keep reading that geometry on every frame. Animate the original and the rig follows by itself. Each layer carries a small block of JSON in its Comment field, prefixed with RIGKIT. It records the rig type, the source layer name, the controller name and the options used. This is what makes Update, Unlink and Remove possible, and it is why those tools can find every related layer from a single selection. Clearing a layer's comment orphans it. RigKit will no longer see it as part of a rig, and Remove will leave it behind.