Apps with 'Outline folding' feature
Dynalist is a web app that lets you break down and organize your thoughts in the format of lists.
Open-source tool for writers. With outliner, character management, plot development, distraction-free editor, etc.
A new medium for your ideas—augment your thinking with a text editor designed for structuring lists. Side-by-side views allow 3 modes of thinking.
OmniOutliner is a start-to-finish writing app. Perfect for collecting information, outlining Big Ideas, adding structure to any sort of writing, and much more.
FoldingText makes you productive in easily formatted plain text. Turn your ideas into plans. Your to-dos into results. Your writing into clear, focused documents.
Visual Outliner is an outliner software for Windows, and it uses OPML as native file format.
It's not just another tasklist application, but a real outliner editor that can be used to write, view, modify, and maintain hierarchically arranged text.
CrossLine is an outliner with sophisticated cross-link capabilities in the tradition of the well-respected Ecco Pro.