One of the random internal projects I've worked on at Clearspring is the tool we use for managing development sprints. Its called TracBoard, and its an interface on top of the open-source Trac ticket management system.
I didn't have any interest in maintaining and using separate systems for defects and detail work as well as for overall task management. So while there are a number of lightweight sprint planning tools out there, and a number of detailed issue-management systems, getting both integrated, with an experience we like, was not in the cards. So I built a relatively simple front-end for Trac data that gives a more whiteboard-style view.
Its not the most robust thing in the world (I built it as a quick internal tool), but hey, it works for us and if there's interest in it, we'll put some more energy into taking it forward for more general use. You can check it out on GitHub.