We needed to be able to group Tickets within Open Atrium as backlog items to be organized into Iterations. After considering ways to emulate that with the stock Open Atrium architecture, I decided to just create the functionality and encode it as a Feature. The result is Open Atrium Iterations.
This is a pretty basic Feature that defines a new content type that has some node reference fields to reference existing nodes in the existing Atrium group. It is completely discrete from Open Atrium's existing Features and structures, so this is something you can just drop in.
Caveats: This is not the be-all project management planning tool. We use OA to communicate with our clients, not for puzzling out our development plan. Our actual planning work is done in a separate saas system. We just needed to be able to communicate our development plans, including iteration definition, to our clients in a way that went a step beyond flat files or manually collected URLs. This Feature allows you to create an Iteration node that simply lists and links to the backlog items in the Iteration, without having to modify existing Features. (We did it this way in hopes that the Feature will survive future releases of Open Atrium without running into conflicts.) You can reference as many existing nodes as you want. The resulting Iteration nodes can in turn be organized using the Books hierarchy. In this way you have a simple tool for communicating your plans to the clients. We use noderefence so that discussion about individual user stories, use cases or feature requirements could be focused in that particular ticket (or blog post or book page, however you prefer to do it).
Rather than add this to our features server, we are moving back to keeping our primary Drupal contributions on Drupal.org. We think this is a good way to go because it can be so hard keeping track of features scattered all over the globe.
Please try out OA Iterations and let me know what you think. If you have any ideas, please use the issue queue! Thanks!