Eric Davis wrote down a handy list of capistrano variables:

• application - required
• repository - required
• scm - defaults to :subversion
• deploy_via - defaults to :checkout
• revision - defaults to the latest head version
• source - Capistrano::Deploy::SCM object
• real_revision
• strategy - Capistrano::Deploy::Strategy object defined by deploy_via
• release_name - timestamp in the form of “%Y%m%d%H%M%S”
• version_dir - defaults to ‘releases’
• shared_dir - defaults to ‘shared’
• shared_children - defaults to [‘system’, ‘log’, ‘pids’]
• current_dir - defaults to ‘current’
• releases_path - path of deploy_to + version_dir (e.g. /u/apps/example/releases )
• shared_path - path of deploy_to + shared_dir (e.g. /u/apps/example/shared )
• current_path - path of deploy_to + current_dir (e.g. /u/apps/example/current )
• release_path - path of releases_path + release_name (e.g. /u/apps/example/releases/20100624000000 )
• releases - list of releases, found by running ls -x
• current_release - path of releases_path + last release (e.g. /u/apps/example/releases/20100624000000 )
• previous_release - path of releases_path + previous release (e.g. /u/apps/example/releases/20100623000000 )
• current_revision - revision id of the current release, found in the REVISION file
• latest_revision - revision id of the latest release
• previous_revision - revision id of the previous release
• run_method - either :run or :sudo depending on if :use_sudo is set
• latest_release - release path or the current release depending on if the current symlink is valid