this may be old and certainly wont be a secret in 3 days but here is a *rumored* list of the API improvements to Leopard according to AeroXperience: Complete 64-Bit support for Intel and PowerPC through all frameworks excluding QuickTime C, QuickDraw, Sound Manager, Code Fragment Manager, Language Analysis Manager and QuickTime Musical Instruments. These modules are deprecated and one should use the modern equivalents instead. Leopard will feature resolution-independent user interface and there are several functions to get the current scaling factor and apply it to pixel measurements. It is a good idea to use vector controls and buttons (PDF will work fine) or to have multiple sized resources, similar to Mac OS X icon design, so you can scale to the nearest size for the required resolution. Address Book adds support for sharing accounts, allowing an application to restrict content according to user. Automator includes a new user interface and allows things such as action recording, workflow variables and embedding workflows in other applications. Time Machine has an API that allows developers to exclude unimportant files from a backup set which improves backup performance and reduces space needed for a backup. A new Calendar Store framework allows developers access to calendar, event and task information from iCal to use in their applications or to add new events or tasks. Carbon, the set of APIs built upon Classic MacOS and used by most 3rd party high-profile Mac OS X applications, now allows Cocoa views to be embedded into the application. This could provide applications like Photoshop and Microsoft Office access to advanced functions previously only available to Cocoa applications. A new control for creating matrices of views is available, NSGridView. This allows a grid to be created from any view in the system, including OpenGL or Web Views. Core Animation allows layers to be used as backing stores for a view, windows to use explicit animations when resizing (can be three dimensional, akin to the Time Machine view). Any view can now be put into fullscreen mode and a CoreImage transition effect can be used. Using Core Animation you can create anything including GPU-accelerated Front Row-style user interfaces without having to write OpenGL code. A Core Animation layer can include OpenGL content, Core Image and Core Video filter effects and Quartz/Cocoa drawing content, like views and windows. Text engine improvements include a system wide grammar checking facility, smart quote support, automatic link detection and support for copying and pasting multiple selections. Core Image has been upgraded to allow access to RAW images directly. Apache 2.0, Ruby on Rails and Subversion are included, and support for script-to-framework programming is available, allowing Python and Ruby scripting to access Mac OS X specific APIs. The iChat framework allows a developer to add shared content to an active iChat session, for example a video, an image slideshow or even an online multiplayer game. "Sharing accounts" are possible, with users being restricted via an access control list (ACL) to certain applications or files. Developers can integrate with this by restricting access to a specific piece of content by connecting it to a sharing account. Sharing accounts have no home folder. An Image Kit is included, to allow a developer to easily create an application that can browse, view, crop, rotate and pick images, and then apply Core Image filter effects through an interface. A slideshow interface is also open to developers, allowing any application to display a fullscreen slideshow of images. Leopard also gives developers access to a "Latent Semantic Mapping" framework, which is the basis for spam protection in Mail. It allows you to analyze text and train the engine to restrict items with specific content (like spam e-mail for example). Mail stationery is open to developers, allowing any web designer to create fantastic-looking Mail templates, with defined areas for custom user content. A new framework is included for publishing and subscribing to RSS and Atom feeds, including complete RSS parsing and generation. Local feeds can be shared over Bonjour zero-configuration sharing and discovery. Quicktime 7.1 is included, and the underlying QTKit framework is greatly improved. There is improved correction for nonsquare pixels, use of the clean aperture which is the "user-displayable region of video that does not contain transition artifacts caused by the encoding process", support for aperture mode dimensions, improved pitch and rate control for audio and a number of developer improvements, like QuickTime capture from sources like cameras and microphones, full screen recording or QuickTime stream recording. Live content from a capture can be broadcast as a stream over the network.