Wikipedia
YXA
YXA is a program written in Erlang implementing a telephone private branch exchange (PBX) was written by Magnus Ahltorp at Royal Institute of Technology (KTH) in the end of 2002. In February 2003, Fredrik Thulin of Stockholm University joined in, working on new functionality and RFC compliance. It implements Voice over Internet Protocol (VoIP) services. Its name comes from Ericsson PBX systems called AXE. Axe translated to Swedish is YXA.