As pointed out by Tonymacx86, Apple has released the Open Source code of OS X 10.10 Yosemite, otherwise known as Darwin 10.10.0. This includes the xnu-2782.1.97 kernel.
The update occurred last night and is available to anyone who wants to root around Apple’s open source code.
Darwin is an open sourceUnix-like computer operating system released by Apple Inc. in 2000. It is composed of code developed by Apple, as well as code derived from NeXTSTEP, BSD, and other free software projects.
Darwin forms the core set of components upon which OS X and iOS are based. It is mostly POSIX compatible, but has never, by itself, been certified as being compatible with any version of POSIX. (OS X, since Leopard, has been certified as compatible with the Single UNIX Specification version 3 (SUSv3).