Ekiga (formely known as GnomeMeeting) is an open source VoIP and video 
conferencing application. Ekiga uses both the H.323 and SIP protocols.
It supports many audio and video codecs, and is interoperable with other 
SIP compliant software and also with Microsoft NetMeeting.

This package will be built without gnome (nor avahi) support. This will 
break the Help button (probably because it requires the gnome help system) 
but it is not otherwise very useful.

This requires pwlib and opal (both available at SlackBuilds.org).