Outliners

Org Mode (also: org-mode; ) is a mode for document editing, formatting, and organizing within the free software text editor GNU Emacs and its derivatives, designed for notes, planning, and authoring. The name is used to encompass plain text files ("org files") that include simple marks to indicate levels of a hierarchy (such as the outline of an essay, a topic list with subtopics, nested computer code, etc.), and an editor with functions that can read the markup and manipulate hierarchy elements (expand/hide elements, move blocks of elements, check off to-do list items, etc.).

word processor and outliner

thumb|350px|An outline in Emacs [[Org-mode.]] An outliner (or outline processor) is a specialized type of text editor (word processor) used to create and edit outlines, which are text files which have a tree structure or a tree view, for organization. Textual information is contained in discrete sections called "nodes", which are arranged according to their topic–subtopic (parent–child) relationships, like the members of a family tree. When loaded into an outliner, an outline may be collapsed or expanded to display as few or as many levels as desired.

Logseq is a free and open-source, personal knowledge base and note-taking application which can store data locally. It supports both Markdown and org-mode syntax.