title: Which issue trackers support sub-tickets, and how well do they work for bridging the gap between project managers and developers?
body: <p>There's a feature that I'd like to see in issue tracking software that just doesn't seem to be all that common, and that is the ability to divide a ticket (bug, feature request, etc) into sub-tasks and view them in a hierarchical fashion, perhaps with some kind of progress bar style report of progress on a particular ticket and its child tickets.</p>
  
  <p>My thinking is that this would be useful for both developers and project managers: project managers like to have a fairly broad overview of what is going on, whereas developers need to drill down to the details, and very often need to divide a task into sub-tasks. This would also come in handy if someone put two issues into one ticket.</p>
  
  <p>Does anyone know of an issue tracker which does this? So far the ones I've looked at (Trac, FogzBugz, and Basecamp) all have a flat organisation of tickets, so they're either useful for the developers or for the project managers but not for both. <a href="http://www.assembla.com/" rel="noreferrer">Assembla</a> does allow a ticket to have child tickets (and multiple parent tickets) but it doesn't do a very good job of usability on this specific feature.</p>
  
  <p>If there is such an issue tracker, has anyone used it for both developers and project managers, and if so, how much success did you have with it? Alternatively, is there a better approach that can be usable by both categories of users?</p>
  
  <p>(<strong>Update:</strong> This is <em>not</em> a subjective "what is your favourite bug tracking software" question. I am asking about bug trackers with a specific feature for a specific purpose, so please don't post your favourite bug tracker if it doesn't do what I've asked for. The only arguably subjective element is how well it works for this particular purpose.)</p>