Community contributions

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Domain Group
This module provides integration between Domain and Group modules.

Entity Group field
provides a computed field that can be configured on any entity types that are associated with Groups. Thus allowing viewing and editing of group associations directly in such entities.

Group Actions
This module adds configurable actions regarding Group functionality, such as adding a user as member, adding or removing content.

Group Authorization consumer
Allows mapping Authorization providers, like LDAP groups, to Group membership.

Group Block
This module is designed to associate group specific block content with a group when using the Group module.

Group Bulk Operations
This module creates an Action plugin that can assign/update a user's group role for multiple groups at once.

Group Comment
This module is designed to associate group specific comment content with a group when using the Group module.

Group Commerce
Combine Group module and Commerce module (Many feature hasn't be completed).

Group Contact
Provides personal contact form integration for the Group module.

Group Content Field
Add opportunity to manage group content under target entity.

Group Content Menu
The difference between this module and Group Menu is mainly in its data model. That module creates everything as menu config items. This creates everything as content entities.

Group Entityqueue
This module is designed to associate entity queue entities with a group when using the Group module.

Group Extras
Add gids field on each entity type which been enabled in group. Auto update the above gids filed value when a group content been inserted or deleted.

Group Finder
This module is an API module that allows you to find group in different scenarios.

Group Forum
Private forums for groups.

Group Hierarchy
Allows you to view the groups and their hierarchy.

Group Invite
Allows group managers to invite people into their group.

Group Mapping From Node
This module adds a configuration section to a node form to select a Group and make it part of it.

Group Media
This module is designed to associate group specific media elements with a group when using the Group module.

Group Member Management
This module provides more-granular permissions to groups for managing group memberships.

Group Membership Request
This module allows users to request a membership to a group and managers (administrators) to approve these requests..

Group Menu
This module is designed to associate group specific menus with a group.

Group Node Field
This module aims to allow the association of Group Content to a Group(s) via the node form.

Group Notify
Notify (email) members of a Group when new group content is posted via Group Node plugins.

Group permissions parameter
This module provides API to set group permissions on the group level using Group permissions module based on custom parameters (e.g. field in the group). Setting the permissions of a group is executed when saving it.

Group Profile
Enable members of a given group to view each other's profiles.

Group Purl
This module provides Purl plugins to support Group
module. With this module, it is easy to make a Group-based site that keeps the group context for views, adding content, and browsing through a group.

Group Roles Management
Allows to adding new permissions to manage roles.

Group Taxonomy
This module is designed to associate taxonomy vocabulary entities with a group when using the Group module.

Group Workflow Integration
This module is a bridge between the group module, the group content submodule and the Workflow module.

Maestro Group Security
This module incorporates Group membership and roles with maestro workflows.

Subgroup
Allows you to set up a hierarchy of groups, with permissions inheriting up or down the tree.

Subgroup (Graph)
Provides an alternative graph mechanism to create hierarchy of groups.

Views Add Button: Group
This module contains the custom routing information needed to build Group and Group Content add buttons as a part of the Views Add Button project.

Under Development 

Code may be available in a sandbox or on github.

Group Book Integration (status as of 2019-01-10: sandbox)
The Group module by default ignores the hierarchical nature of Book pages. This module changes that by ensuring that when a Book is added as group content, its book pages are automatically added as well; when a Book is removed from a group, its book pages are removed as well.

Group Role Delegation
This module allows group owner to grant specific roles to users.
User can set expiry date for selected roles, expiry dates are controlled by cron job, so it automatically removes any expired roles.

Group VBO
Assign nodes to Groups and remove nodes from Groups in bulk.

Message Group Notify
Group notifications integration for Message Stack

Not yet ported to Drupal 8