Native support by many libraries and frameworks for 64-bit applications, allowing 64-bit Cocoa applications. Existing 32-bit applications using those libraries and frameworks should continue to run without the need for emulation or translation.
Leopard will offer the Objective-C 2.0 runtime, which includes new features such as garbage collection. Xcode 3.0 will support the updated language and was itself rewritten with it.
A new framework, Core Animation, allows a developer to create complex animations while specifying only a "start" and a "goal" space. The main goal of Core Animation is to enable the creation of complex animations with small amounts of program code.
Apple has integrated DTrace from Sun's OpenSolaris and added a graphical interface called Xray. DTrace provides tools that users, administrators and developers can use to tune the performance of the operating system and the applications that run on it.

The new Scripting Bridge allows programmers to use Python and Ruby to interface with the Cocoa frameworks.
Leopard supports resolution independence, the ability to size system graphics in physical units such as centimeters or inches instead of pixels. This feature results in standard size graphics independent of the device on which they are viewed. Preliminary support was added in Mac OS X 10.4 to prepare developers for a "future release of Mac OS X."
Leopard’s OpenGL stack has been updated to version 2.1, and will use LLVM to increase its vertex processing speed.

Apple has been working to get LLVM integrated into GCC; Usage of LLVM in other parts of the OS has not been announced.
Leopard’s security frameworks support Mandatory Access Control, sandboxes and code signing.
The Graphics and Media State of the Union address confirmed many other features possible because of Core Animation, such as live desktops, improvements to Quartz Composer with custom patches, a new PDF Kit for developers, and improvements to QuickTime APIs.
A fairly new patent from Apple refers to a new way of rendering desktop backgrounds or live desktops. The method involves a set of pre-written instructions, or recipe for rendering the desktop image. In this way desktops can now appear on the screen organically and are not stored in the RAM or VRAM leaving it free for other use.[29] This is not a confirmed feature and may not be included in Leopard.
In mid-December 2006 a pre-release version of Leopard appeared to include support for Sun's ZFS.
While Apple has not confirmed or denied speculation that ZFS would be included with Leopard, Jonathan Schwartz, CEO and President of Sun Microsystems, stated on June 6, 2007 that ZFS has become "the file system" for Leopard.

However, the senior project marketing director for Mac OS X stated on June 11, 2007 that HFS+, not ZFS, will be used in Leopard.

Apple has since clarified that a 'read-only' version of ZFS would be included.

Compatibility
Like Mac OS X 10.4, Leopard will support both PowerPC and Intel Macs. However, Leopard will not be released in separate versions, but instead will comprise one universal release that will run on either processor. While it is known that Leopard will support PowerPC G4 and PowerPC G5 processors, support for the PowerPC G3 is reportedly not present in the pre-release versions which have been made available to developers.When Apple’s Leopard website first appeared online, the 64-bit section stated, "From G3 to Xeon, from MacBook to Xserve, there is just one Leopard." The sentence was removed from the page the following day, leaving open the question of whether Leopard will support Macs with G3 processors.In the past, each new major release of Mac OS X has dropped support for at least some older Macs; 10.3 dropped support for Macs without built-in USB ports, and 10.4 dropped support for computers without FireWire ports.

Documentation contained with the Developer Preview DVD states that a PowerPC G4 or G5, or Intel processor is a minimum requirement. Despite this, some users have managed to install the developer preview version of Leopard on Macs with G3 processors by editing a particular file and then creating a new installation DVD with this edited file. However, even though these installations of Leopard can be installed on G3 Macs, some applications (for example Safari and iChat) will not run.[36] It is not known whether this will be possible with the final shipping version of Leopard.

Leopard is fully UNIX compliant. Certification means that software following the Single UNIX Specification can be compiled and run on Leopard without the need for any code modification.