I first started using an outliner in the late 1970s, on Unix. It was character-based, on a scrolling display. You'd type commands like
1,$p to show all the lines at the current level. You could view the subs of any headline, by typing the number next to it, and pressing Return. The basic operations were "dive" and "surface." Moving things around was a little more difficult, but it was the best you could do with the computers of the day.
The tools advanced through the years. Influenced by Visicalc, then Lotus 1-2-3. That's when the outliner got a "bar cursor" which points to a structure, much like Visicalc's cursor points to a spreadsheet cell. You moved the cursor around with the arrow keys, and expanded by pressing < and collapsed by pressing >. These keys were chosen as mnemonics, they looked symbolically like the operations they were performing.
Pretty soon after that we got the mouse, so you could double-click to expand and collapse and also drag things from one place to another. This made stuff flow better. That's a key idea -- outlines are about flow, they make text fluid (i.e. able to flow).
Then came graphics, and with that bullet charts and tree charts. All of a sudden there was a production application for outliners, they could be made to do things more efficiently on a computer than could be done with ink, paper and scissors. The business exploded.
All along, I have been writing code and prose with the outliner. These days I use it to narrate my work and to coordinate with the people I work with. It's an amazingly flexible swiss-army-knife-like super-adaptable tool.
I've been doing a lot more with outliners in the last few months, in a project I've been working on with a new programming partner, Kyle Shank, at a new company we founded late last year, Small Picture. It has both a server side and a client side. Next week we will show the first bits of the client software. I think it will surprise people what it can do and how it does it. But this wouldn't be a good tease if I told you more about what it is. :-)
In the meantime, if you have stories to tell about how you love outlining, please consider posting them. I love outliners, but I love outliner users even more. They're such bright people and so incredibly powerful and creative. Software that enables powerful people.
So much more to say and I hope to say it all.