KissXML provides a drop-in replacement for Apple's NSXML class culster in environments without NSXML (e.g. iOS).
It is implemented atop the defacto libxml2 C library, which comes pre-installed on Mac & iOS. But it shields you from all the nasty low-level C pointers and malloc's, and provides an easy-to-use Objective-C library.
It is designed for speed and reliability, so it's read-access thread-safe and will "just-work". That is, KissXML provides an API that follows "what-you-would-expect" rules from an Objective-C library. So feel free to do things like parallel processing of an xml document using blocks. It will "just work" so you can get back to designing the rest of your app.
SDK for Apple
Better Swift generated interface cross-compatibility with NSXML by matching NSXML headers more closely, specifically by changing many set/get methods to properties.