- 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
