RadioBox is open-source broadcasting solution that relays on client-server architecture. It consists of media server that runs as a service and listens for socket connections of graphical interfaces (web access, Windows GUI, Linux GUI, etc...)
Open Source IM and voice client using Jabber and SIP protocols, with great audio quality thanks to speex and a nice and clean interface. Programmed in Java and C++. It supports chat, voice and file transfers.