• Cross-platform: runs anywhere Tcl/Tk runs (I have used it on linux and Windows and it has been reported to work on Mac OS 9.2)
• Multiple outlines supported using a tabbed notebook interface
• Inter-outline hyperlinks using wiki syntax (see Wiki-like hyperlinked outlines) allowing for the creation of a web of outlines.
• Hyperlinking to parts of an outline
• External URL hyperlink support
• Support for bold, italics, underline, and strikethrough formatting
• Drag and Drop movement of nodes
• "Size" of each collapsed node is displayed
• Available as a single file "starpack" distribution (standalone executable), or two file "starkit" distribution. No installation needed.
• Relatively small--can fit on a single floppy disk.
• Export to ascii, html, xml, opml
• Import from indented text, opml
• Save subtree, load tree as subtree
• Key bindings are externally configurable
• Mode-less - i.e. there isn't a separate mode for editing vs. for navigating the outline headlines.
• User scriptable. See scripting tkoutline, outline widget and Magic button functionality.

Behaves similar to a text editor:

• Headlines are alway "active" and cursor movement between headlines is smooth
• Headlines can be split at the cursor into two adjacent headlines by hitting the enter key
• Two adjacent headlines can be merged by hitting delete at the end of a line or backspace at the beginning of a line

Screenshot:

Older screenshots

Screenshot of the multiple outline version (same as the old screenshot, except there are tabs across the top for each file and example hyperlinks are shown):

Here is a screenshot of the older single outline version (version 0.61 and earlier): ghttp://tkoutline.sourceforge.net/tkoutline1.png