OpenH323 is a multi-platform H323 Video Conferencing library.

This can be used to make H323 Video Conferencing applications.
and the port produces a sample application called OhPhone.

OhPhone can exchange full duplex audio and video with other H323
compliant video conferencing programs including Microsoft NetMeeting
It requires a sound card for audio support and a Bt848/878 based
video card (using the bktr driver) for video capture.

The OpenH323library, and ohpone makes use of PWLib.
PWLib is a multi-platform code library that can be used to write
applications that will compile and run on the BSD Unixes, Windows, Linux
and a few other Unix variants. It was developed by Equivalence Ltd Pty.

For more information see
http://www.openh323.org
http://www.equival.com