One thing an outliner lets you do that you can't do with something like Wave or a tree structured discussion group is to arbitrarily rearrange the tree.

You're right, you can represent tree-structured outlines in Word or Docs (or JSON in Excel or Sheets as I described here [1]), but it's clumsy and not well supported by the user interface.

[1] Representing and Editing JSON with Spreadsheets: https://medium.com/@donhopkins/representing-and-editing-json...

Where Frontier really shines is in its user interface and feature set, which makes navigating and creating and editing outlines very easy and efficient.

Frontier's main use was (tree structured) content management and scripting, and making websites is a popular application of that. It was extremely useful for making tools, and like Emacs, its power came from its extensibility.

Its pre-web predecessors [2] were ThinkTank (which started on the Apple ][ with a keyboard based interface) and MORE (which added a mouse-based drag-and-drop interface, that made it much easier to use without spoiling the ease of use of the keyboard interface, and also formatted graphics for making charts and slide shows).

[2] MORE (application): https://en.wikipedia.org/wiki/MORE_(application)

Beyond obvious stuff like content management, blogging, and scripting, I think there are many other killer applications of programmable outliners (just as emacs and spreadsheets have many applications), some old hat, and others undiscovered!

I wrote some more [3] about Dave Winer's work on Frontier, and linked to some screencasts he made that show how he uses it to organize his thoughts (about the history of outliners, in this case, which is beautifully self-referential).

I think the most important point that comes through in Dave's demos is that the operating system and user interface shell should support generic outlining and scripting at a very basic, built-in, ubiquitous level. But I believe Windows, OS/X, iOS and Android have a hell of a long way to go!

[3] https://news.ycombinator.com/item?id=20672970

Dave Winer's second outliner screencast:

https://www.youtube.com/watch?v=mgUjis_fUkk

Dave Winer's the many lives of Frontier screencast:

https://www.youtube.com/watch?v=MlN-L88KScw

Dave Winer on The Open Web, Blogging, Podcasting and More:

https://www.youtube.com/watch?v=cLX415mHfX0

>UserLand's first product release of April 1989 was UserLand IPC, a developer tool for interprocess communication that was intended to evolve into a cross-platform RPC tool. In January 1992 UserLand released version 1.0 of Frontier, a scripting environment for the Macintosh which included an object database and a scripting language named UserTalk. At the time of its original release, Frontier was the only system-level scripting environment for the Macintosh, but Apple was working on its own scripting language, AppleScript, and started bundling it with the MacOS 7 system software. As a consequence, most Macintosh scripting work came to be done in the less powerful, but free, scripting language provided by Apple.

>UserLand responded to Applescript by re-positioning Frontier as a Web development environment, distributing the software free of charge with the "Aretha" release of May 1995. In late 1996, Frontier 4.1 had become "an integrated development environment that lends itself to the creation and maintenance of Web sites and management of Web pages sans much busywork," and by the time Frontier 4.2 was released in January 1997, the software was firmly established in the realms of website management and CGI scripting, allowing users to "taste the power of large-scale database publishing with free software."