I found another excellent, free, 2-pane outliner like Keynote NF. It's called ToDoList
http://www.abstractspoon.com/tdl_resources.html. It is almost project management software too. It has all kinds of features: filters, alarms, rich text editor, etc. Besides the main developer, others have made a calendar plug-in and a Gantt chart plug-in for the app.
I almost overlooked ToDoList because I did not learn and test it long enough the first time I looked at it...so be sure to give it a thorough look. You can customize the GUI so that you just see the outliner and Comments window, or you can have it show other columns; such as, "start date", "finish date", and a number of other columns. The developer is active and regularly updating the app. ToDoList seems rock solid...I could find no bugs. However, the downside is that it is written in C++; so it is only available on the Windows platform. I guess you could run it on the Mac if you use Parallels. I have been looking for and testing outliner software continuously for 30 years, and this is one of the best...in my opinion.
Yet another super 2-pane (and 3-pane) outliner is Scrivener
http://www.literatureandlatte.com/. This one was developed for the Mac, but they now have a PC Beta version. The Mac version is $45. The PC version is free now...but will be $40 when released. This one is being used by professional writers and has won all kinds of awards. The neat and unusual thing about this app is that you can open two rich text editor windows and an outline window all together. They made the app this way so that you can edit and see a research window and outline along your writing window and outline at the same time.
and the project is still active. Just in a certain stand-by, simply because of a great workload I have actually.