1984-87 System 1. 0 through 4. 1: Introduced the Macintosh's graphical-user interface. 1987 System 5: MultiFinder enables more than one...
System 1.0 through 4.1: Introduced the Macintosh’s graphical-user interface.
System 5: MultiFinder enables more than one application to run at once. Color QuickDraw brings color graphics.
System 6: Solidified MultiFinder and supported 32-bit processing of larger RAM.
System 7.0: Built-in cooperative multitasking (instead of MultiFinder), aliases, AppleScript, virtual memory, Balloon help.
System 7.1: Fonts folder, QuickTime.
System 7.5: Apple Guide help system, Stickies, WindowShade, QuickTime 2.0, support for PowerPC processor in Power Macintosh, LC and Performa models.
Mac OS 8: Multithreaded Finder, Platinum visual appearance.
Mac OS 8.1: Last version to run on Macintoshes with 68K processors, optional HFS Plus file system, PC Exchange for reading Windows files.
Mac OS 8.5: Ran only on PowerPCs, Sherlock search system, QuickTime 3.0, ran on first iMacs.
Mac OS 8.6: Operating system nanokernel features multitasking, multiple processors.
Mac OS 9: Open Transport networking, multiple-user environments, iTools, (now .Mac), Carbon libraries in anticipation of Mac OS X.
Mac OS X 10.0 (Cheetah): First release of new operating system built on Unix foundation, Aqua interface, multiple users, native PDF support.
Mac OS X 10.1 (Puma): Bug fixes, speed improvements, more stable.
Mac OS X 10.2 Jaguar: First version to incorporate code name into product name, iChat, Sherlock 3, Rendezvous auto-configuring networking, Quartz Extreme hardware-based graphics processing.
Mac OS X 10.3 Panther: Fast User Switching, Exposé, Power Mac G5 support.
Mac OS X 10.4 Tiger: Spotlight system-level search, Dashboard, QuickTime 7, Automator, H.264 video codec, 64-bit processor architecture.
Sources: Wikipedia (en.wikipedia.org/-
wiki/Mac_OS), TidBITS (www.tidbits.com)