The Apache Portable Runtime (APR) is a supporting library for the Apacheweb server. It provides a set of APIs that map to the underlying operating system (OS). Where the OS does not support a particular function, APR will provide an emulation. Thus programmers can use the APR to make a program truly portable across platforms.
GLib – provides similar functionality. It supports many more data structures and OS-independent functions, but fewer IPC-related functions. (GLib lacks local and global locking and shared-memory management.)
^Stable Apache Release Hits, Sean Michael Kerner, 2 December 2005, "Apache Portable Runtime (APR) 1.0 API, which provides libraries that interface between the underlying operating system and the server."