title: Which open source, extensible, potentially easy to use issue-tracker? redmine, trac, bugzilla, mantis, RT?
body: <p>Looking for an issue tracker for a medium-sized web application open project with a distributed team. We are planning to run this on our own server. It must be very easy for new users to submit new issues, and it must integrate well with other software.</p>
  
  <p>Our major requirements, in descending order of importance:</p>
  
   <ul><li>open source</li>
   <li>capable of very new-user-friendly bug submit
   <ul><li><b>submitting new issue must be as easy as possible</b>, with only a single screen to fill out (after registration), and few fields visible (e.g. just "summary" and "description" would be good)</li>
   <li>Google Code is an example of the sort of interface we like; Bugzilla's Bugzilla instance (https://bugzilla.mozilla.org/enter_bug.cgi) is an example of the sort of new bug submit interface that we would NOT like</li>
   <li><b>it's fine if the default submit interface is not new-user-friendly as long as this is easily modifiable</b> using templates/skins. It would be great to have an "advanced view" for bug editing with additional fields (such as who the issue is assigned to), in addition to the simple view for new user bug submission</li>
  </ul></li>
   <li> has API; or, supports other applications concurrently accessing its db backend (we want to <b>query and modify the issues from other, separate software</b> running on another server)</li>
  </ul>
  
  <p>Other desirable criteria, in descending order of importance:</p>
  
  <ul>
   <li> not frustrating in daily use</li>
   <li> has a relatively <b>large community</b></li>
   <li> integrates well with <b>hg (mercurial)</b></li>
   <li> <b>amenable to integration</b> with external:<ul>
   <li> support desk/request tracking software</li>
   <li> project management software</li>
   <li> auth systems (and/or supports OpenID login)</li>
  </ul></li>
   <li> modular; if we modify the issue tracker, we want to release those improvements as a module that is easy for others to install</li>
   <li> amenable to having some sort of simple, easy-to-use issue importance voting system, e.g. stars on Google code; we intend create or modify such a component to plugin to our own external voting system</li>
   <li> amenable to integration with SugarCRM</li>
  </ul>
  
  <p>When I say "amenable to", I mean that we are willing to code an extension to the issue tracker ourselves if necessary, however, the issue tracker's architecture should be amenable to that sort of extension.</p>
  
  <p>Issue trackers which also include support desk or project management features are a plus provided that we can choose to integrate external software instead of using the included stuff. We don't need another wiki (we already have one that we like).</p>
  
  <p>According to Google searches (see the comments), the most popular open source issue trackers are trac, bugzilla, mantis, RT (and possibly Launchpad's). I've also included Redmine because I've never seen a recent comparison between any of these issue trackers and Redmine in which someone had something bad to say about Redmine, and on polls Redmine sometimes beats these others. Feel free to suggest others (bearing in mind that one of the criteria is "relatively large community").</p>
  
  <p>There are undoubtedly multiple good issue trackers out there; many of those listed above claim to be extensible and integrable with other software. What would be most helpful would be direct comparisons between issue trackers by people who have used more than one.</p>
  
  <p>How do these compare to each other on <strong>extensibility, integratability, and skinnability</strong>? </p>
  
  <p><strong>If you have used more than one of these, which of them would you recommend</strong>, and which others have you used?</p>
  
  <p>Which of these are <strong>already integrated</strong> with a large number of auth systems/support desk systems/etc? </p>
  
  <p>Comments explaining why a particular popular open-source issue tracker (especially one of those listed above) is NOT suitable for our situation are very welcome; this will save me time.</p>
  
  <p>thanks!</p>