Twinkle (software)
Twinkle is a free and open source software application for Voice over Internet Protocol (VoIP) voice communications in IP networks, such as the Internet. It is designed for GNU/Linux operating systems and uses the Qt toolkit for its graphical user interface. For call signaling it employs the Session Initiation Protocol (SIP). It also features direct IP-to-IP calls. Media streams are transmitted via the Real-time Transport Protocol (RTP) which may be encrypted with the Secure Real-time Transport Protocol (SRTP) and the ZRTP security protocols.
Since version 1.3.2 (September 2008), Twinkle supports message exchange and a buddy-list feature for presence notification, showing the online-status of predefined communications partners (provider-support needed).
Read more about Twinkle (software): Supported Audio Formats