ohmybrain
uddeIM 
uddeIM allows users of your community to send Private Messages to each other (note that uddeIM is not a webmail component nor an email client). uddeIM wants to be simple and easy-to-use but it offers all the features you need in a Private Messaging System ...
Kunena
Kunena - The leading Joomla Forum Component. Downloaded more than 1,850,000 times in 3 years since its start. The only forum/discussion solution for Joomla that is community driven. No hidden fees, no surprises - true open source. See our public forums, G ...
Fabrik
Fabrik is THE open source Joomla application builder component. Fabrik gives you the power to create forms and tables that run inside Joomla without requiring knowledge of mySQL and PHP. Then feed your data into Google Maps, Charts or an AJAX based cal ...
JomSocial
JomSocial is an award-winning social networking component for Joomla. Create your own Social Network with Photo and Video Gallery, Event Management, Activity Stream and other features that work out of the box. JomSocial features: * Friendship system f ...