Asterisk is a software implementation of a telephone private branch exchange (PBX); it was created in 1999 by Mark Spencer of Digium. Like any PBX, it allows attached telephones to make calls to one another, and to connect to other telephone services, such as the public switched telephone network (PSTN) and Voice over Internet Protocol (VoIP) services.
FreeSWITCH is free and open source communications software for the creation of voice and messaging products. It is licensed under the Mozilla Public License (MPL), a free software license. Its core library, libfreeswitch, is capable of being embedded into other projects, as well as being used as a stand-alone application.