User Referral Enhanced
This module allows users to generate referral links that can be shared anywhere. When someone uses a referral link to create an account, the owner of the link is credited with a record of the referral. The module supports multiple referral types and can be extended by other modules.
This module helps to generate referral links which can be shown anywhere in site and can be shared with others, over email messages or other methods. Whenever that referral links are used and visitors create user account. Then this module credits the referral link owner by creating a record to indicate the referral to that new user.
This module got created to overcome the limitations of User Referral module. Mainly, that module does not have facility to pass extra information with referral link.
Other modules can extend this module to generate various types of referral links of their business logic and site needs.
Drupal 8+
Drupal 8+ version of this module has built in support to create multiple referral types.
3.x releases
2.x versions of this module do not work with 3.x releases of the extra_field_plus module. You would need to use 3.x release to make it work with extra_field_plus 3.x.
You would also would be required to reconfigure the referral links displaying in user profiles after installing the 3.x releases.