sleek is a todo.txt manager, free and open-source (FOSS)
The Freeplane add-on that syncs a GTD mind map with a todo.txt file
MNoteLite is a simple todo manager
Piggydb helps you have more fun with knowledge creation.
Where do you want to shop today? Deluxe Manager for Shoppinglists.
Create a task list while making minutes with OpenOffice or LibreOffice