Contrary to what the name suggests, XMeeting is Mac software (and not X Windows software) for videoconferencing. I just tried it tonight to call my friend Martin Brooks at NRC and it worked very well. It even gets around my firewall (NAT) without any problem. Oh? Did I mention it was open source? Looks like some kind of GPL-incompatible FreeBSD-like license.
As with all things, there is a catch under Mac OS with the use of the camera. If you are using the camera in one application, for example, XMeeting, then it becomes unavailabe under other applications such as skype. However, you may get the misleading error message ‘No video camera connected’. Simply ensure that you have only one camera-using application opened at any one time.