Mac OS X Panther (version 10.3) is the fourth release of macOS, shipped on October 24, 2003. Its signature was Exposé — one key scattering every open window into a live overview — an instant-classic answer to window clutter that rivals spent years imitating, and the ancestor of Mission Control. Safari became the default browser (Internet Explorer for Mac quietly exiting), and the brushed-metal Finder gained a sidebar and fast user switching's rotating-cube flourish.

Security grew up alongside: FileVault encrypted home directories, and the built-in firewall gained a face.

Exposé; fast user switching; Safari as default; the sidebar Finder with labels; FileVault; Font Book; iChat AV video conferencing; Xcode's debut as the developer environment; and Windows-domain integration for offices.

Exposé changed how people think about window management across every desktop OS, and Panther's polish-plus-speed cycle (it ran faster than Jaguar on the same hardware, a pattern users came to expect) marked the platform's maturity. Xcode's arrival established the toolchain every Apple platform still builds on.