Seven is a direct backport of the default Drupal 7 core administration theme (designed by Mark and Leisa).
Note: Navigation is severely crippled in this theme without the D7 toolbar. For that reason, it's recommended that you use an administration navigation module such as Toolbar, Administration menu, Admin, Teleport, or Navigate.
The Seven theme is already a part of Drupal 7 core, so naturally this project will never have a Drupal 7 version. Just download Drupal 7!
Before upgrading to Drupal 7, be sure to disable this theme and physically remove it from the file system to avoid conflicts. You may also like to remove the theme settings from the database, which can be done with this Drush command:
drush vdel theme_seven_settings -y
...or this SQL:
DELETE FROM variable WHERE name = 'theme_seven_settings';