Joomla 1.5 has an alternative to Community Builder and Jomsocial.
KickApps is basically a wide-ranging set of social networking tools, including videos, photos, audio, user profile, blogs and the other usual social goodies.
Why did KickApps choose Joomla? According to the founder’s blog, a key reason was customer demand. Lots of Kickapps users were already using Joomla and wanted more advanced integration.
Sample site: Training for Warriors