macOS Catalina (version 10.15) is the sixteenth release of macOS, shipped on October 7, 2019 — the platform's rip-the-bandage year. iTunes, eighteen years old and carrying Apple's whole media history, split into Music, Podcasts, and TV; 32-bit applications stopped launching entirely; and the system moved onto its own read-only volume. Sidecar turned an iPad into a Mac display, Catalyst opened iOS app porting to all developers, and Screen Time crossed from iOS.

The breakage — dead 32-bit apps and games, aggressive new permission prompts, notarization requirements — made Catalina the era's most complained-about upgrade, and "wait for the point releases" its lasting advice.

Music/Podcasts/TV replacing iTunes; the read-only system volume; Sidecar; Mac Catalyst; Screen Time; Find My (merged); Voice Control accessibility; Apple Arcade; and activation lock on T2 Macs.

Catalina cleared the ground the Apple-silicon era was about to build on — pure 64-bit, sealed system, notarized software — absorbing the anger so Big Sur could arrive clean. The iTunes split ended the defining software of the iPod age; the 32-bit cutoff remains the line that divides Mac software history.