Variable module provides a registry for meta-data about Drupal variables and some extended Variable API and administration interface. The idea of this module is to provide some API for contributed modules to declare their variables so other modules, like Internationalization, can use this information to translate them, build customized settings forms, export groups of variables, etc...
The module has been extended with some other features that include an administration interface for variables, Variable Admin, a storage module, Variable Store, support for multiple variable realms and lately with support for Domains and Multilingual variables per domain.