The Open Settlement Protocol (OSP) standard defined by the European Telecommunications Standards Institute (ETSI TS 101 321) www.etsi.org. . The OSP Toolkit is an open source implementation of the OSP peering protocol and is freely available from www.sourceforge.net. It enables applications for secure multi-lateral peering. . libosptk development library and header files for building OSP client end applications with OSP Toolkit.