Tuleap is the best project lifecycle management system, it facilitates agile software development, design projects, V-model, Requirement Management, and IT Services Management. It is the best open source application and has lot features and it is also integrated with ldap.

Great GUI, complete and beautiful. Free to use and open source. Easy to use and manage.

Tuleap is an easy all-in-one simple tool: you can track your tasks, manage your documentation and code versionning, write & execute tests, be Agile or V cycle, with one interface. Many of the available services are available out of the box. Some, like the Trackers, can be fully customized which is really nice since you can really adjust the data you want the user shall fill in, you can force the tasks workflow or not, etc. There is also a highly powerfull rights management included. You can also do requirements tracing with the Trackers. They also provide a monthly update of the tool, and offer a very reactive customer feedback service for those who have an Enterprise edition (and they also reply to any request they receive even if you have a community edition).