GTDTree is a commercial Windows organizer application based on the GTD principles. It is a lightweight and fast utility, storing data locally on your computer in XML files, giving the users the ability to create simple lists of items in a more sophisticated way.
You can manage many different item entities using the GTDTree, such as contexts, projects, goals and other GTD related stuff, appending them hierarchically into an outline which is the basic view of the application. However there are more views you can switch to on the fly, filtering items by their entity type. So regardless of their position into the outline you can have a view with all tasks, projects, goals and even a view with an integrated calendar.
Adding items is quick and easy, using shortcut keys, and items can be moved in the hierarchy by simple drag and drop. Items can have due dates and can occur for once or repeatedly.
The implementation shares the same style as my Life organized outliner, in a more simple way. The user interface is good in general providing various themes, but the icons should been designed more carefully, for they are ruining the big picture and the whole work of the developers. Also the icons cannot be customized and there is no password protection ability for the files you create.
There is no mobile application yet, but as the developing team states it will be available sometime later but there is always the benefit of using single files which can easily be synchronized across computers with a file sharing service like Dropbox.
There is a free/lite version of GTDTree which can hold up to 50 items and you can purchase the full version with $46. The good thing is that you can try it first since the only limitation of the demo version is the maximum number of items you can create.
If you prefer having your todo lists locally than sharing them on the web, you should give it a try.