Apps with 'Outline folding' feature

Zim brings the concept of a wiki to your desktop. Store information, link pages and edit with WYSISYG markup or directly typing some lightweight markup syntax and see it previewed as-you-type. Creating a new page is easy by either clicking on the "Create new note"...

Free, open-source note-taking with rich text, cross-platform support, syntax highlighting, embedded files, and customizable interface.

Open-source writing tool with hierarchical outliner, distraction-free editor, character management, plot development, Snowflake method, and writing goal support.

Dynalist is a web app that lets you break down and organize your thoughts in the format of lists.

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. From grocery lists to email drafts to long-form composition.

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.

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.

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.

CrossLine is an outliner with sophisticated cross-link capabilities in the tradition of the well-respected Ecco Pro. It implements the concept of "Transclusion" proposed by Ted Nelson and - among others - implemented in the legendary Objectory SE tool by Ivar Jacobson.