Garland was removed from Drupal core as of Drupal 8 as part of the Platform Initiative. This project is meant as a fork of the Drupal core's version of Garland to keep Garland alive and kickin'.
The Equi Join module allows you to create relationships between different entities based on an arbitrary field. This allows the use of relationships in Views without having to add Node References to a content type, which may not be an option when displaying data stored on a third-party database or data provided through custom Views handlers. That said, it works with nodes as well.
As an example, if you have a content type Employee and another content type Department, and they both have a different field that contains their Department ID, you can create a View that links them both by means of the Department ID field. In very simplified terms, the resulting query would be something like (note that the fields for the ON clause can be different as long as they contain similar data to join on):
SELECT *
FROM employee
LEFT JOIN department
ON employee.field_employee_deptid = department.field_department_id;
The above query will retrieve all the employees with their associated departments.