Quite apart from external links, many outliners support internal links as well. A simple implementation uses Web-like hypertext to take you to another place in the outline, or even in another outline reachable by your machine. A more complete implementation doesn’t have the limitations of the Web, and might allow two-way linking, named and typed links, and links among text bocks and headers.

Tinderbox is the champ in this department too. Links can be from or to blocks or text. They can be typed, overlap, and have agents and tags attached. The now defunct Palimpsest had a similar, less capable (no agents) set of links, but they could be two-way.

The example screenshot for this feature is VooDooPad, which is in effect a two-pane outliner without the first pane, and which implements the hierarchy as links. Better is a similar capability in Hog Bay Notebook which supports both this “wiki”-type hyperlink and the traditional hierarchy.