Sugar Cube Software's open-source CocoaSpriteKit has reached Beta release 2.

Built from ground up using Objective-C and Mac OS X's Quartz Compositing
Engine, Cocoa Sprite Kit is a framework designed to make powerful 2D
graphics applications with ease. Although mainly designed for 2D games,
developers are encouraged to find more creative uses.

The Cocoa Sprite Kit (CSK) was inspired by Cocoa, valuing ease of
development and rich high level frameworks and functionality. Developers
can write Cocoa applications and get features such as transparency,
scaling, rotation, and other graphics transformations, collision detection
and graphics layering with a minimum of programming effort. CSK is designed
for both new and experienced programmers who want to focus on program logic
/ game-play instead of low level blitters and other graphics problems.

Interested developers are welcome to provide feedback and/or participate as
future contributors to the project.

Beta 2 brings improved screen saver support, a formal plugin architecture
for games written with CSK, a run time debugging tool, native Bezier path
based sprites, as well as many other improvements and bug fixes.

More information, including all source code, sample applications, and
preliminary documentation can be found on the website
(http://www.sugarcubesoftware.com/csk).