libss7 is a userspace library for providing SS7 protocol services to applications. It has a working MTP2, MTP3, and ISUP for ITU and ANSI style SS7, but was written in a manner that will easily allow support for additional national specific variants in the future. For a working reference implementation, see the various link test programs, as well as the Asterisk Open Source PBX.
VoxForge collects transcribed user-submitted speech audio files (collectively called a "speech corpus") to create acoustic models for use with speech recognition engines such as HTK, Julius, ISIP, and Sphinx. The current focus is on collecting audio to create acoustic models for command and control applications on a PC, and for voice over IP telephony speech recognition applications, i.e. IVR (Interactive Voice Response).
Sipcat is a software IP telephony system that helps businesses increase productivity and reduce telecommunication costs. It allows you to start running your own voice over IP PBX in a matter of minutes. It contains a complete Linux distribution, including Asterisk and all required 3rd party software.
Mediastreamer is a portable C library that allows you to create and run audio and video streams. It is designed for any kind of voice over IP applications. It features RTP connectivity, audio codecs (Speex, iLBC, G711, GSM, and AMR), video codecs (MPEG4, H263, H264, and Theora), sound card I/O, wav file streaming, webcam video capture, echo-cancellation, conferencing, parametric equalization, and various other utilities. It has a modular design that makes it extensible through plugins. This is the media-streaming component of linphone, a GPL SIP video phone.