Roles and visibility

Who can do what in a tracker.

Owner controls the tracker: members, settings, archive and delete. There's exactly one owner.

Editors run threads day to day: add, edit, assign, close, move and delete any thread. They can invite people up to contributor.

Contributors add threads and comments, and edit, close or delete only the threads they created or that are on them.

Commenters read and comment. They can close a thread only if it's on them.

Viewers are read-only and can't be given threads.

Separately, visibility can be set to 'only sees what they add'. Those people never see anyone else's threads.