The open source version of the Mac operating system from Apple, which allows developers to make their own improvements. Darwin is based on the Mach microkernel and various Berkeley Software Distribution (BSD) versions of Unix. Although Darwin has been available as source code since 2000, the programming interface (API) source code is not, however, open and free to use. From 2002 to 2006, a community-based OpenDarwin project existed, which was followed by PureDarwin in 2007. See
macOS.