APR (Apache: The Definitive Guide, 3rd Edition)

20.2. APR

APR is the Apache Portable Runtime. This is a new library, used extensively in 2.0, that abstracts all the system-dependent parts of Apache. This includes file handling, sockets, pipes, threads, locking mechanisms (including file locking, interprocess locking, and interthread locking), and anything else that may vary according to platform.

Although APR is designed to fulfill Apache's needs, it is an entirely independent standalone library with its own development team. It can also be used in other projects that have nothing to do with Apache.