State makes extensive use of the Apache Portable Runtime. APR is a portability layer developed for use by the Apache web server to hide non-portable code away from the server's core. It provides a very useful API for developing C based server software. State uses every feature that APR provides so that the software remains as portable as possible, or as portable as Apache anyway. For more information on APR, see the APR web site at http://apr.apache.org/.