TCPCam is a free, simple to use, setup, hack, video conference software for the Linux operating system. It basically takes the video stream from a video4linux device, and the audio from the sound board using the OSS API, and uses a single TCP port in order to forward this data to a remote host (and the reverse).
Because raw video and raw audio are too big in order to ensure a fluid conference experience, TCPCam uses the JPEG compression algorithm and the Speex encoder in order to compress audio and video data. This makes you able to use the audio part even with a modem, and the video+audio with a decent DSL line. Note that you can use TCPCam in audio-only or video-only mode if you like.
TCPCam uses a very simple non-standard protocol. The link between the two hosts is a single TCP (on port 7766 for default). It is required that at least one of the two computers involved has this port open in order to start a conference. The TCPCam protocol is very simple and it should be trivial to create an application compatible with this protocol. The protocol description is available inside the tar.gz of the application (the file called PROTOCOL)
TCPCam is Free Software, distributed under the GPL License.