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.
Selenio helps you manage your reminders in an extremely quick way
...In case you decide to snooze the alarm, you'll have many predefined options: just choose one and click on it!
Selenio is a cross-platform application: it's written in python and uses the wxPython framework, so it can be used on Linux, Windows and Mac OS/X.
Selenio is an open-source application and is licensed under the terms of of the GNU General Public License Version 2.