Core Foundation (also called CF) is a C application programming interface (API) written by Apple Inc. for its operating systems, and is a mix of low-level routines and wrapper functions.
[1] The most prevalent use of Core Foundation is for passing its own primitive types for data, including raw bytes, Unicode strings, numbers, calendar dates, and UUIDs, as well as collections such as arrays, sets, and dictionaries, to numerous macOS C routines, primarily those that are GUI-related.
At the operating system level Core Foundation also provides standardized application preferences management through CFPropertyList, bundle handling, run loops, interprocess communication through CFMachPort and CFNotificationCenter, and a basic graphical user interface message dialog through CFUserNotification.
[2] Apple used to release most of CF as an open-source project called CFLite that can be used to write cross-platform applications for macOS, Linux, and Windows.
[5] A fork of OpenCFLite was created by Grant Erickson (an original collaborator with Brent Fulgham on the SourceForge version) in 2021[6] with a companion port of the CFHost portion of CFNetwork, as OpenCFNetwork.