Mac OS X Public Beta

Mac OS X Public Beta is the original public beta for Mac OS X 10.0 released in retail by Apple on 13 September 2000. This version marks the debut Aqua UI and the Darwin operating system kernel. It is also one of the few instances where a software beta has appeared in retail stores.

Development
Following the failure of the Copland and Rhapsody projects intended to ease transition from classic Mac OS operating systems and a new generation of Mac OS systems, Apple announced the creation of the Carbon API at a 1998 Worldwide Developers Conference (WWDC). Carbon was intended to provide backwards compatibility to running classic Mac OS applications under the existing NeXTSTEP kernel instead of being emulated under the "Blue Box". Carbon would be demonstrated running in a Rhapsody build during the event and would be planned to be implemented in a future version.

After the announcement to convert Rhapsody to a server-released operating system, development would be split between reworking Rhapsody and creating an operating system with the Carbon API. Shortly after the release of Mac OS X Server 1.0, the first Developer Preview was distributed to developers who participated in a 1999 WWDC on 10 May 1999. The conference also demonstrated the Carbon implementation on Mac OS, running a legacy Finder application concurrently with a mail application developed with the native Cocoa libraries. Apple intended to release another developer preview in late 1999, while releasing the final operating system in early 2000.

Despite releasing the second Developer Preview on time during 10 November 1999, the third Developer Preview showcased during the MacWorld Expo 2000 would unveil a new Aqua theme for the first time to the public on 14 February 2000. The Developer Preview also demonstrated the Dock, a prominent feature in the Mac OS X interface. A fourth and final Developer Preview would be shown on a 2000 WWDC on 15 May 2000. The Public Beta would release on 13 September 2000, followed by an international release that supports more languages on 21 October 2000.

Mac OS X Public Beta is known for being the first version to be built on the Darwin operating system core. This enabled protected memory and preemptive multitasking, increasing overall kernel stability. Although the Public Beta was met with initial immense hype from users prior to its release, it received mediocre reviews from critics and developers, owing to compatibility issues and lack of driver support compared to Mac OS 9. The final release of Mac OS X Public Beta, known as Mac OS X Cheetah, would later release on 24 March 2001. 14 May 2001 would mark the expiration date for the Public Beta; any portion of the Aqua interface would no longer function after the timebomb date. Testers who have purchased the Public Beta were qualified for a $30 discount on the final Cheetah release.