Houseparty - Brining empathy to online communication.
SocialEngine - Socialengine PHP: Elevating Your Online Community Experience.
Booyah - Video chat with up to 12 friends at the same time.
mooSocial - mooSocial is the best social network script to create a niche community or social site.
Slack - A messaging app for teams who see through the Earth!
JomSocial - Open Source Social Networking Software. Award winning open source community software by JomSocial. This social networking software is widely used by many Joomla users.