Sky field module has grown up from Node field module.
It provides wider and more flexible functionality.
Sky field module allows you to add unique custom fields to any single Drupal entity (node, user, comment and etc).
It's not connected to fields module, so different entities of one entity type can have absolutely different sets of custom fields.
1) Install Sky field module.
2) Go to admin/config/sky-field. Select entity types to use sky field module.
3) Now you can add unique custom extra fields to your entities.
UI is made the same way as in fields module. Many hooks were added, so now it can be used as a base for more complex modules.
You can add new sky field types using hook_sky_field_info_alter. You can change fields widgets and formatters. And so on!
We have tried to make it as flexible as possible!
It's beta version now, so we are grateful for any feedback!