Free flexible open source todo manager featuring hierarchical tasks
...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.
A complete Getting Things Done (GTD) productivity system for desktop a
Mindwtr: The Privacy-First GTD System
Mindwtr is a Getting Things Done (GTD) productivity tool designed for "Mind Like Water." It runs completely offline—no accounts, no tracking, and no subscriptions.
The Core GTD Workflow
Capture: Instantly offload thoughts to your Inbox.
Clarify: Process tasks rapidly with the built-in "2-Minute Rule" timer.
Organize: Sort tasks by Contexts (@work, @home), Areas, and Projects.
Reflect: Keep your system trustworthy with a guided Weekly...
Ukolnicek is a multi-platform (Windows, Linux, OS X) PIM tool. It allows to keep all your personal task in a graphical and easily accessible form to help manage your time efficiently. Using synchronization you can access your data from everywhere.
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.