If you're not looking for a full-blown 3D rendering engine, SpriteKit can help you create a cool AR experience without having to understand the complexities of rendering a 3D world. SpriteKit is Apple's two-dimensional game rendering engine. Some of the biggest game titles on iOS are actually SpriteKit apps, so even though it's not a full 3D rendering engine, it's still a really powerful framework that you can use to build great games and AR experiences.
Similar to how ARKit and SceneKit work together, Apple has created some classes that you can use to replace regular SpriteKit classes. In the case of SpriteKit, a scene is normally rendered in a SKView. If you use SpriteKit to create an AR experience, you replace SKView with an instance of ARSKView. An ARSKView is tied to an ARSession and can render ARAnchors similarly to how SceneKit does. You can provide normal SKNode instances and they will automatically be rendered in the scene.
One major difference between SceneKit and SpriteKit is that SpriteKit is a 2D rendering engine. This means that any objects that you place in a SpriteKit scene are only rendered in two dimensions. In practice, this means that you can't view a rendered SKNodes from all sides like you would be able to do for a 3D model. A SKNode will always face towards the user, but event though SpiteKit is two-dimensional, all nodes are placed in the three-dimensional world. Because of this, you can place an object before or behind another object or behind the user. This behavior enables you to create an immersive experience, even if you aren't using 3D models.
Since we'll be using SpriteKit to build our AR gallery, let's take a closer look at SpriteKit to get you up to speed with the information you need to make use of SpriteKit in your own applications.