Real, dated releases and announcements — verified against official sources, not speculation.
Released to retail October 25, 2001, Windows XP was the first consumer edition of Windows built on the NT kernel rather than the MS-DOS-based 9x line — ending the split between Windows 9x/Me and Windows NT/2000 for good.
First previewed under the codename Monad in 2003, renamed Windows PowerShell in April 2006, and finally released to the web that November — replacing decades of cmd.exe-centric scripting with a genuine object-oriented shell.
Released August 24, 1995, Windows 95 brought the Start menu and taskbar to the mainstream — backed by one of the largest software marketing campaigns ever mounted, including a Rolling Stones-licensed ad and Jay Leno at the Redmond launch event.
Released August 28, 2009, Mac OS X Snow Leopard was the first version built exclusively for Intel Macs — a deliberate stability and performance release rather than a showcase of new user-facing features.
On May 18, 2007, Leopard on Intel Macs became the first BSD-based operating system to earn Open Brand UNIX 03 certification — making 'Mac OS X is a real Unix' a certified fact, not just a technical argument.
Released September 13, 2000 for $29.95, the 'Kodiak' public beta gave Mac users their first hands-on look at preemptive multitasking, protected memory, and the Aqua interface before the final 10.0 release.
On January 22, 2007, the Open Source Development Labs and the Free Standards Group combined into the Linux Foundation, consolidating Linux's economic and standards-setting efforts under one organization.
When kernel developers lost free access to the proprietary BitKeeper in April 2005, Torvalds responded by writing an entirely new version control system himself — Git's first commit landed within days.
Released March 14, 1994 at 176,250 lines of code, version 1.0 was the point Linus Torvalds and the community considered the kernel stable enough for production use.
First released August 30, 2012 after two years of development, pkgng consolidated FreeBSD's fragmented package tools into a single command backed by a real database — and became official in FreeBSD 10.