By far the best ToDo list I have ever used.
Pivotal Tracker is great for managing projects and laying out what features need to be done. I do feel that it lacks on the 'what needs to be done for each feature' department, but that can be solved with Asana.
- pivotaltracker.com
- Pivotal Tracker.app - Fluid app to make the Pivotal Tracker web interface seem like a native OS X App.