SupportCandy Usergroup Addon GPL Overview:

You may have customers which is an organization or company and require multiple people to create tickets and each other’s tickets should be visible in between themselves then this is the right solution for you. You can create unlimited usergroups with unlimited members. Members checked as supervisors can see and manage tickets created by all members of the group. Whereas members not checked as supervisors can only see their own tickets just like normal reporter do.