This project develops video conferencing and VoIP applications for Mac OS X. XMeeting is based on the work of the OpenH323 project which provides the libraries for H.323 and SIP support.
Lion is out for ages now, and Xmeeting keeps crashing (as it was under 10.6) -- a defunct app
I tried for a large fraction of an hour to connect to my employer's Codian bridge, but each time I tried to enter the conference number or passcode, at least one digit got duplicated. There is no backspace. Unusable.