1984-87

System 1.0 through 4.1: Introduced the Macintosh's graphical-user interface.

1987

System 5: MultiFinder enables more than one application to run at once. Color QuickDraw brings color graphics.

1988

System 6: Solidified MultiFinder and supported 32-bit processing of larger RAM.

1991

System 7.0: Built-in cooperative multitasking (instead of MultiFinder), aliases, AppleScript, virtual memory, Balloon help.

1992

System 7.1: Fonts folder, QuickTime.

1995

System 7.5: Apple Guide help system, Stickies, WindowShade, QuickTime 2.0, support for PowerPC processor in Power Macintosh, LC and Performa models.

July 1997

Mac OS 8: Multithreaded Finder, Platinum visual appearance.

January 1998

Mac OS 8.1: Last version to run on Macintoshes with 68K processors, optional HFS Plus file system, PC Exchange for reading Windows files.

October 1998

Mac OS 8.5: Ran only on PowerPCs, Sherlock search system, QuickTime 3.0, ran on first iMacs.

May 1999

Mac OS 8.6: Operating system nanokernel features multitasking, multiple processors.

October 1999

Mac OS 9: Open Transport networking, multiple-user environments, iTools, (now .Mac), Carbon libraries in anticipation of Mac OS X.

March 2001

Mac OS X 10.0 (Cheetah): First release of new operating system built on Unix foundation, Aqua interface, multiple users, native PDF support.

September 2001

Mac OS X 10.1 (Puma): Bug fixes, speed improvements, more stable.

August 2002

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.

October 2003

Mac OS X 10.3 Panther: Fast User Switching, Exposé, Power Mac G5 support.

April 2005

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)