Swift
Apple's replacement for Objective-C — Chris Lattner (the LLVM creator), 2014, open source since 2015. Statically typed, protocol-oriented, automatic memory management via ARC.
Compiles to LLVM IR. New features: async/await (5.5), actors, structured concurrency, regex literals, macros (5.9). SwiftUI (2019) replaced AppKit/UIKit for Apple platform UI. The Swift on Server initiative (Vapor, AWS Lambda) keeps it alive on Linux.
Dominates iOS/macOS/watchOS/visionOS development. Outside the Apple ecosystem adoption is marginal. Competitor there: Kotlin Multiplatform.