The quest completer will complete bugged quests for you so you can turn them in. You can check if quest is bugged in game using command .qc $questlink, where $questlink is shift-clicked quest from your quest log.
If you have a quest which is not completable due to a bug and don't see it here, please visit the Bug Tracker and report it there. Be sure to report quests that are still in the list but already fixed as well.
You need to log in to use this tool