The core Liquibase source code is at http://github.com/liquibase/liquibase.
All standard extensions are a part of the http://github.com/liquibase.
Liquibase is designed to support adding, enhancing, and overriding standard functionality through our extension framework. Often times, the best way to add new functionality is to create a new extension or add to an existing one rather than modifying the base library.
For more information on how to write extensions, see the extension portal.
Bugs and features for the core Liquibase project are managed at http://liquibase.jira.com/browse/CORE.
For more information, see Liquibase Jira Workflow
Issue tracking for extensions are handled as they see fit.
For more information, see the individual extension pages on the the extension portal.