Ask HN: What are some must know xcode / obj-c topics / libraries?

I'm trying to step up my iOS game to be competent + have the ability to use the appropriate libraries / tools when building any type of iOS app. Some topics + tools that I've already used w/ obj-c + xcode: -auto-layouts -cocoapods -afnetworking -post / get -fmdb -json handling -location manager -mantle -RNCryptor -singletons -blocks -Segues -kiwi testing -spritebuilder What are some other must know topics / libraries / tools (e.g. webview optimization tips, running an app in the background etc..)?