Rightsized recommends this tool for keeping track of the SCRUM product backlog. I'm going to use it as neither Sharepoint nor Google Spreadsheets has been a perfect fit.

Quoted: Rally Software – Scaling Software Agility with Project Management, Requirements Management, Test and Defect Tracking Software Tools and Coaching for Agile Development Teams

Might be worth a try.

Quoted: The $1000 price tag attached to Microsoft Project Pro got you down? Cross platform open source app OpenProj comes to the rescue. OpenProj markets itself as a complete replacement for Microsoft Project and boasts complete integration with existing Project files and Primavera.

I do like that a top-level datatype in basecamp is the milestone. Todo lists, message, files, specs, etc. can all be included as part of the milestone. On the negative side, the one feature I was looking for -- a hierarchal view of all the workitems for the cycle -- seems to be missing.

Quoted: People working together on projects need a way to share project data. There are emails, meeting appointments, assigned tasks, and files to share among project members. In addition, appropriate access must be granted to internal managers and external stakeholders such as clients. While Microsoft Project, Project Server and Project Web Access are designed for complex enterprise projects, many organizations and project teams don't need the sophistication of Microsoft Project, and do not want to manage and administer such a system

some more on scrum...

Quoted: Scrum naturally focuses an entire organization on building successful products. Without major changes -often within thirty days - teams are building useful, demonstrable product functionality. ...

Quoted: The team meets daily for 15-minute standup meetings and then they go off to work on their portions of the project. And although there is ...