CallWeaver is a community-driven, vendor-independent, cross-platform, open source, PBX software project (formerly known as OpenPBX.org). It was originally derived from Asterisk. Now it supports analog and digital PSTN telephony, multi-protocol voice over IP telephony, fax, software-fax, T.38 fax over IP and many telephony applications such as IVR, conferencing and callcenter queue management. Source: CallWeaver