Coming in under the radar, Apple has released a new preview version of their Apple CarbonLib SDK. Version 1.2d2 adds a number of bug fixes and improvements, and allows developers to build Carbon apps or port existing apps to the Carbon layer of OS X.
The SDK (Software Developer Kit) works on Mac OS 8.6 or greater, and is immediately available to Apple Developer Connection members. Interested users may sign up to become ADC members at the Apple web site.