FreeSWITCH

Sofia-SIP is an open-source SIP User-Agent library, compliant with the IETF RFC3261 specification.

SpanDSP is a low-level signal processing library that modulates and demodulates signals commonly used in telephony, such as the "noise" generated by a fax modem or DTMF touchpad.

Unofficial GNU awk for Windows

Unofficial SQLite amalgamation builds

Abstraction