video conferencing
Ekiga
Ekiga (formely known as GnomeMeeting) is an open source VoIP and video conferencing application for GNOME. 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.
Dimdim Open Source
Dimdim is an open source web meeting product with features like Application, Desktop and Presentation sharing with audio and video conferencing and chat. No attendee installation - all features are available through a web browser. Dimdim can be integrated with Moodle.
WengoPhone
WengoPhone allows you to make PC to PC video and voice calls, and to integrate all your IM contacts in one place. Please note that WengoPhone do not integrate yet Video Conferencing.
Openmeetings
Multi-Language Cross-Platform Customizable Video-Conferencing and Collaboration