We have a very large user database using Community Builder. After installing CiviCRM, it doesn't appear to be recognizing any of the data from Community Builder. Is there a migration tool or procedure to import that data into CiviCRM?
I've never used it and don't know whether it functions with current versions of CiviCRM, but there is (or was) a tool that seems related to what you are asking (although maybe just synchronizing going forward, not for existing contacts): Joomla 2 CiviCRM User Synchronization
This plugin integrates the Joomla and/or Community Builder registration process with CiviCRM.
Newly created Joomla website users (from Joomla or Community Builder frontend or backend) will be matched with existing CiviCRM contact(s) based on their email address. If no matching CiviCRM contact is found, a new one will be created and synchronized with the Joomla user. The plugin can also be configured to attatch and assign a new CiviCRM activity to the contact.
If that's not a good solution, you may be able to prepare or download a CSV file from Community Builder and do an import to CiviCRM manually.