The single user version of TreePad X Enterprise has been released on December 17th. While Treepad comes in several different versions, most will probably be acquainted the freeware version, Treepad Lite, which also has recently been updated (December 11).
As they say: "TreePad Lite (freeware) and TreePad Asia (freeware) are small and powerful personal database programs, only 600 Kb in size. They allow you to store all your notes, emails, texts, hyperlinks, etc. into one or multiple databases. With the look and feel of the familiar Windows explorer, editing, storing, browsing, searching and retrieving your data can not be easier! ... [They] can be run directly from a floppy, if necessary, including data. To find any article you previously created or imported, you can browse the tree, in the same way as you browse directories/folders in the Windows explorer. You can also use the internal search engine to find any piece of information swiftly." It stores information in what is essentially a text file.
I am a registered user of TreePad Business, which adds some interesting features to the free version, most notably rtf support and convenient hyperlinking of notes. It also plays well with ConnectedText's URLs and allows me to integrate the two applications. (I have even beenfound a way to store entire (and very large) ConnectedText projects in TreePad Files.
Treepad Business my favorite two-pane outliner, which I use to store "static" information, i.e. documents for reference, etc.
I also licensed the single-user version of Treepas X, which uses SQL, but I do not like it very much because it does not interact well with AutoHotKey—something to do with the way it interacts with the clipboard (I think).
I have tried many two-pane outliners, but I always go back to Treepad Business edition