Nobody's mentioned Ecco Pro, at least as far as I could find! It's a Windows based PIM that has an excellent outliner built in to it. As a PIM it's fairly complex to learn, but as an outliner, it was a breeze to learn and is delightful to use. I use it for planning projects and brainstorm an idea or set of tasks.

Unfortunately it, like seemingly all other effective outliners (Grandview, ThinkTank, Info Select etal), has been abandoned by it's last publisher, NetManage, Inc. The NetManage site doesn't even list it as one of their products, but they do have a webpage you can directly access (http://www.netmanage.com/products/Eccopro that has links to the latest, almost 2 years old(!), update to EccoPro 4.01. It appears that on 1/30/98 they were willing to sell additional licenses to existing users. Don't know if you can buy a copy today though. I'm glad I've got mine.

If seems to me that a form of outlining is build into many different programs today. As a result software publishers apparently don't see a need to publish a standalone product with the simple functionality and ease of organization (like in ThinkTank or More) that an outliner provides. I guess they think outlining is covered by what's included in Word or PowerPoint or Project. Even EccoPro was not marketed as an outliner. I know I work more effectively because I use the outliner in EccoPro to plan projects and think through ideas. Those other programs don't come close to providing the simple functionality of a good outliner.

Info Select? Although I think that it's a wonderful program, it's not an outliner and its still being sold by Micrologic. Perhaps you were thinking of Lotus Agenda?

I used and liked Ecco for years. You are right, the outlining was easier than the other PIM features. And it is exactly that integrated outlining that I miss in other products. Notably Outlook! Outlook notes are just begging for outlinging capability. Without it, they are just electronic post-its (that is not a compliment!).