Twinkle is a softphone for your voice over IP and instant messaging communcations using the SIP protocol. You can use it for direct IP phone to IP phone communication or in a network using a SIP proxy to route your calls and messages.

Sofia-SIP is a SIP User-Agent library, compliant with the IETF RFC3261 specification. It can be used as a building block for SIP client software foruses such as VoIP, IM, and many other real-time and person-to-person communication services.

GNU ccRTP is an implementation of RTP, the real-time transport protocol from the IETF. It is suitable both for high capacity servers and personal client applications. It is flexible in its design, allowing it to function as a framework for the framework, rather than just being a packet-manipulation library.

LibiLBC is a packaging friendly copy of the iLBC codec from the WebRTC project. It provides a base for distribution packages and can be used as drop-in replacement for the non-free code from RFC 3591.

LibIAX2 implements the Inter-Asterisk-Protocol for relaying Voice-over-IP (VoIP) communications.

PJProject provides an implementation of the Session Initiation Protocol (SIP) and a multimedia framework.

GNU Common C++ is an portable, optimized class framework for threaded applications, supporting concurrent synchronization, inter-process communications via sockets, and various methods for data handling, such as serialization and XML parsing. It includes the uCommon C++ library, a smaller reimplementation.

A collection of libraries and header files for implementing telephony functionality into custom Telegram clients.

SpanDSP is a library of DSP functions for telephony, in the 8000 sample per second world of E1s, T1s, and higher order PCM channels. It contains low level functions, such as basic filters. It also contains higher level functions, such as cadenced supervisory tone detection, and a complete software FAX machine.

GNU uCommon C++ is meant as a very light-weight C++ library to facilitate using C++ design patterns even for very deeply embedded applications, such as for systems using uclibc along with posix threading support.

GNU oSIP is an implementation of the SIP protocol. It is used to provide multimedia and telecom software developers with an interface to initiate and control SIP sessions.

xgoldmon is an utility that converts the USB logging mode messages that various Intel/Infineon XGold modems send to the USB port to gsmtap. It then then sends them to a given IP address to enable users to view cellular network protocol traces in Wireshark.

It supports the following smartphones:

• Samsung Galaxy S4, GT-I9500 variant

• Samsung Galaxy SIII, GT-I9300 variant

• Samsung Galaxy Nexus, GT-I9250 variant

• Samsung Galaxy SII, GT-I9100 variant

• Samsung Galaxy Note II, GT-N7100 variant

GNU ZRTP C++ provides a library that adds ZRTP support to the GNU ccRTP stack and serves as library for other RTP stacks (PJSIP, GStreamer).

Baresip is a portable and modular SIP user agent with support for audio and video, and many IETF standards such as SIP, SDP, RTP/RTCP, STUN, TURN, ICE, and WebRTC.

Phonesim is a modem emulator that oFono uses for development and testing. This allows oFono to be used by any host without requiring special GSM (or other) hardware.

EXosip is a library that hides the complexity of using the SIP protocol for multimedia session establishment. This protocol is mainly to be used by VoIP telephony applications (endpoints or conference server) but might be also useful for any application that wish to establish sessions like multiplayer games.

Seren is a simple VoIP program based on the Opus codec that allows you to create a voice conference from the terminal, with up to 10 participants, without having to register accounts, exchange emails, or add people to contact lists. All you need to join an existing conference is the host name or IP address of one of the participants.

Mumble is an low-latency, high quality voice chat software primarily intended for use while gaming. Mumble consists of two applications for separate usage: mumble for the client, and murmur for the server.

Libre is a portable and generic library for real-time communications with async IO support and a complete SIP stack with support for protocols such as SDP, RTP/RTCP, STUN/TURN/ICE, BFCP, HTTP and DNS.

This package provides callaudiod, a daemon to route audio during phone calls, and a library.

Libptytty is a small C/C++ library to manage pseudo-ttys in a uniform way, created out of frustration over the many differences of PTY/TTY handling in different operating systems.

In addition to mere PTY/TTY management, it supports updating the session database at utmp, and wtmp/lastlog for login shells.

It also supports forking after start-up and dropping privileges in the calling process. This reduces the potential attack surface: if the calling process were to be compromised by the user starting the program, there would be less to gain, as only the helper process is running with privileges (e.g., setuid/setgid).

Libvterm is an abstract C99 library which implements a VT220 or xterm-like terminal emulator. It doesn't use any particular graphics toolkit or output system, instead it invokes callback function pointers that its embedding program should provide it to draw on its behalf. It avoids calling malloc during normal running state, allowing it to be used in embedded kernel situations.

Libtermkey handles all the necessary logic to recognise special keys, UTF-8 combining, and so on, with a simple interface.

Cool-retro-term (crt) is a terminal emulator which mimics the look and feel of the old cathode ray tube (CRT) screens. It has been designed to be eye-candy, customizable, and reasonably lightweight.