Free flexible open source todo manager featuring hierarchical tasks
Task Coach - Your friendly task manager. Task Coach is a free open source todo manager. It grew out of frustration about other programs not handling composite tasks well. In addition to flexible composite tasks, Task Coach has grown to include prerequisites, prioritizing, effort tracking, category tags, budgets, notes, and many other features. However, users are not forced to use all these features; Task Coach can be as simple or complex as you need it to be. Task Coach is available for Windows, Mac OS X, and GNU/Linux; and there is a companion iOS app.
ToDoBee is a simple yet powerful task management application for Mac OS X. It is a user friendly and intuitive application that can be used for any IT related project as well as any general day to day task tracking/management situation.