Grouptool is another new plugin developed by AMC Academic Moodle Cooperation which enhances the functionality of Moodle default groups. Two of the additional features are the possibility for students to enroll themselves in groups with waiting lists, and the transfer of grades within groups.
Acc. to the plugin description:
You can download the Grouptool plugin from the Moodle plugins database from this link and here is the complete documentation about using the plugin. The plugin is available for all Moodle versions from Moodle 2.6 onwards.