(Unix, GPL) Voice chat via TCP/IP
Note: I (Riku Saikkonen, the author of voicechat) don't really maintain voicechat anymore, and no one else does either. If someone wants to start maintaining it, please contact me (my address is below).
Voicechat allows transferring bidirectional audio data in almost real time over a TCP/IP network such as the Internet. It is meant for two-person voice conversations, much like the telephone.
Compared to other `net phone' programs like Speak Freely, voicechat is quite primitive. It will probably stay that way, unless someone starts actively maintaining it.
Voicechat requires a Unix system with a sound device and a network connection. The program uses GSM compression (with a free GSM library) and a simple silence-detection algorithm to compress the data sent over the network (via a TCP connection); the bandwidth it uses is about 1400 bytes per second in normal speech (max. 1700 cps plus TCP/IP headers). It should work pretty well in lower-bandwidth networks too, but the pauses in silent parts of speech become longer than they should be.
Voicechat also supports text conversation, much like the common Unix talk. Text and voice work at the same time, bidirectionally.
Of i386/i486 machines, the GSM compression requires a reasonably fast machine (a 486-33 should work, maybe slower ones too). Sound can't be recorded and played at the same time unless your soundcard and its driver supports it.
Voicechat is free software, distributed under the GNU General Public License.
The program should work on most Unix systems with little modifications; it has been tested on at least Linux (the development machines), UnixWare, and a few Suns. Voicechat uses and requires ncurses or plain curses, and the freely available gsm library (libgsm).
Voicechat is available here.