While you can grant read/write access to collaborators on a personal repository, members of an organization can have more granular access permissions for the organization's repositories.
A repository owned by a user account has two permission levels: the repository owner and collaborators. For more information, see "Permission levels for a user account repository."
Organization members can have owner or member roles. Owners have complete administrative access to your organization. Member is the default role for everyone else. For more information, see "Permission levels for an organization" and "Repository permission levels for an organization."