WebKit
Apple's open-source rendering engine. Forked from KDE's KHTML in 2001. Powers Safari, all iOS browsers, Mail, App Store, and many native apps that render HTML.
Apple added its own JavaScriptCore (JSC). Google forked Blink from WebKit in 2013 → they've diverged dramatically since. Thick rendering pipeline phases: parse → DOM → CSSOM → layout → paint → composite. WebKit2 (2010) introduced multi-process architecture (rendering in a separate process, higher security). Lives outside Apple in optional apps: GTKWebKit (Linux), WPE (embedded), Epiphany browser.