||This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (November 2007)|
Outliners are typically used for computer programming, collecting or organizing ideas, as personal information management or for project management. Mind Mappers and Wikis are related types of software.
The principal attribute of outline editors is that they support or enforce the use of a hierarchy of their items.
- Editing: Sound parent-child relationships are enforced when the user modifies the document structure. For example:
- Promoting, demoting, copying, or deleting a parent has the same effect on the children.
- Every item entry must be within one level of its predecessor, such that each item must be a sibling or child of the preceding item (thus, no item can be a grandchild of the preceding item).
- Viewing: The tool enables the user to affect the display by level. For example:
- Applying styles by outline level (e.g., bold all 1st level items)
- Displaying selected levels (e.g., show all 1st and 2nd level items, but none deeper).
- Hoisting an item hides all parent and sibling items; thereby focusing, or zooming in, on a particular branch. De-hoisting again reveals the full outline.
- Search/Filter: The tool displays only items that contain the query terms plus their ancestors (parent, grandparent...) to give them context.
- File import and export: Both the content and structure of outlines are conveyed when files are imported or exported (e.g., from and to tab-indented files).
- Fields/Columns: Items can also have additional fields of information. This data can be shown as columns of data in the outline or as fields in the second pane (see 'Layout' below). Some outliners also allow the user to create custom fields and/or filter on fields.
There are two basic types of outliners: one-pane or intrinsic, and two-pane or extrinsic, each with its strengths and weaknesses.
A one-pane outliner is known as an intrinsic outliner because the text itself is organized into an outline format—individual sections (such as paragraphs) of text can be collapsed or expanded, while keeping others in view. Everything is displayed within a single area, hence the term one pane. One of the strengths of one-pane outliners is that, because the text itself is what is structured and because several nodes of text are visible at once, it is easy to edit across sections. The drawback is that, because the structure is not always visible, there is not as strong an overview of the whole or ability to quickly navigate between sections as with a two-pane outliner. Some word processors, such as Microsoft Word, have an Outline Mode to help with structuring documents.
A two-pane outliner separates structure from content—the structure is extrinsic to the text. A tree structure with node titles is presented in one pane, and the text is shown in another. Since the structure is always clearly shown at all times separately from content, this format allows for a quick overview of the structure, and easy navigation. The drawback is that since only one node's worth of text is shown at one time and navigation has the additional step of crossing panes, the structure is more rigid, making editing across nodes more difficult. This view is similar to many file browsers and email programs (which can be thought of as three-pane outliners). This type of structure is useful also as a document management tool where the second pane is a document in place of textual information.
A one- and two-pane outliner may be combined as a hybrid. This allows multiple notes' text and graphics to be shown at the same time. The organizational power of outline in hybrid is in the parent outline structure, not in the second pane text, making it a very effective structure for topical organization. One additional advantage of hybrid is that single pane can be used as single pane outliner with second pane used for notes or reference tracking.
File formats 
Several file formats support an outline structure natively or encourage the use/creation of outline structures.
- XML - XML's purpose is to aid information systems in sharing structured data
- HTML/XHTML - outlines relatively trivial thanks to nested markup
- OPML - simple XML-based format designed for outlines, but also used for syndication feedlists
- OML - alternative to OPML
- RDF - (various formats) has web-oriented node & arc graph model, can be used for outline subset
- XOXO - dedicated HTML-based microformat for outlines
- CHM - standard Windows format for help, books, etc.
Desktop outliners 
|Acta||Mac OS 9||Single pane outliner, free to download|
|ActionOutline||Windows||Double-pane outliner. Multiple outlines per file, selected via 'worksheet-style' tabs.|
|AllMyNotes Organizer||Windows||Can password-protect file access, supports Skins. Free and Portable editions available.|
|Bonsai (Desktop Edition)||Windows||Designed to synchronise with the Palm OS version of Bonsai|
|Circus Ponies NoteBook||Mac OS X||Single-pane outliner designed to resemble a spiral bound notebook|
|Code Browser||Windows/Linux||folding text editor, can outline source code|
|Deep Notes||Mac OS X||Freeware single pane outliner. Only 1.7 megabytes, runs on OS X 10.4 or later.|
|Ecco Pro||Windows||Freeware outliner. EccoMV add-on for RTF pane.|
|Flashnote||Windows / Mac OS||Freeware outliner with support of notes tree|
|GrandView||MS-DOS||Powerful single-pane outliner dating from the 1980s|
|hnb||Linux/platform independent||Terminal based outliner|
|Idea Cruncher||Windows||Minimalist two-pane outliner|
|Idea Rover||Windows||Research paper outliner|
|In Control||Mac OS 7/8||Vintage outliner from Attain Corp, which could sort or filter outlines according to keywords or metadata attached to each topic.|
|InfoQube||Windows||Two-pane outliner with custom columns, rich-text formatting, and several concepts based on EccoPro.|
|Jot+ Notes||Windows||Two-pane outliner where the 2nd pane supports Rich Text formatting and embedded pictures and objects, such as spreadsheets. One can navigate not only via the topic hierarchy in pane one, but also via hyperlinks in the text of pane two.|
|Jreepad||Platform independent||Compatible with Treepad. Written in Java.|
|KeepNote||Windows/Linux/MacOS||Notes saved in HTML. Written in Python.|
|KeyNote||Windows||Mozilla Public License. No longer supported.|
|KeyNoteNF||Windows||Mozilla Public License. Evolution of KeyNote.|
|Maxthink||Windows 2000, ME, XP, Vista, 7, 8||Venerable MSDOS outliner now in Windows|
|MORE||Mac OS 7/8/9||Classic Mac outliner from the late 1980s & early 1990s|
|MSD Organizer||Windows||Single-pane outliner in the following modules: Contacts, Cards, Budget, Property, Health and Music.|
|MyInfo||Windows||Two-pane, but can emulate basic one-pane outliner as well.|
|myBase||Windows||Tree-based free-form outliner and database system with three panes.|
|Leo||Windows/Linux/MacOS||Python application (uses Qt or Tk for the UI)|
|Neomem||Windows||Three-pane outliner. Website last updated July 2008.|
|Nethnic Pandora||Windows||Tree-based text editor and project management tool|
|NoteCase||Windows/Linux/MacOS||No longer supported.|
|NoteKeeper||Windows||Lightweight freeware two-pane outliner|
|Noteliner||Windows||Lightweight freeware outliner with "to do" capabilities, tagging & tables|
|OutWiker||cross-platform||Desktop wiki and outliner. Notes are stored as a directory tree on disk.|
|OmniOutliner||Mac OS X||Single/double pane outliner with columns and extensive customisation capabilities.|
|Opal||Mac OS X||Single pane outliner, essentially a port of 'Acta' to Mac OS X|
|OrgMode||cross-platform||Emacs outlining mode|
|Outliner Lighto||Windows||Free software, console-based outliner written in FreePascal|
|Redhaven Outline||Windows||Lightweight freeware two-pane outliner|
|Sain Outliner||Windows||Low cost, very simple single-pane outliner|
|Scrivener||Mac OS X; Windows & Linux beta||Flexible content generator for writers; powerful multipane outliner|
|SEO Note||Windows||Free lightweight two-pane outliner|
|The Guide||Windows||Free lightweight two-pane outliner|
|ThinkTank||MS-DOS||Early PC outliner, now abandonware|
|Tkoutline||Platform independent||Written in Tcl/Tk|
|ToDoList||Windows||Free (Eclipse Public License). Portable. Large number of node attributes. French and Spanish versions.|
|Tombo||Windows, Windows CE, Windows Mobile||Minimalistic. Regex search. GPLv2.|
|Total Text Container||Windows||Freeware 2-pane outliner|
|Tree||Mac OS X||A lightweight, horizontally expanding outliner that exports to many formats.|
|Treeline outliner||Windows/Linux||Free 3-pane outliner; 2nd pane shows details of highlighted node, 3rd pane lists details of its children.|
|Treepad||Windows/Linux||Two-pane outliner. Free and paid versions.|
|TuxCards||Linux||Freeware 2-pane outliner|
|The Vim Outliner||cross-platform||Vim plugin|
|UV Outliner||Windows||Free, single pane outliner|
|Vault 3||Windows, Linux, Mac OS X, Android||Free outliner. XML import and export. PDF export. Optional 128-bit AES encryption.|
|Vim Outliner||cross-platform||Vim plugin|
|VOoM||cross-platform||Vim plugin, emulates two-pane outliner. Requires Python and Vim compiled with Python interface.|
|XLnotes||Windows||Microsoft Excel add-in that allows to take notes which contain Word documents, web pages and attachments. Emulates two-pane free form outliner.|
Mobile Device outliners 
|Android Outliner||Android||Sync with Natara Bonsai and Treepad on Windows desktop via USB or DropBox; due-date based filtering; supports multiple outlines. Under active development, with very user feedback-driven feature selection.|
|CarbonFin Outliner||iOS||Outliner for iPhone, iPod touch, and iPad. Web app with synchronization is also available.|
|Circus Ponies NoteBook for iPad||iOS||Port of Circus Ponies NoteBook to the iPad.|
|NoteLynX||Android||Features Multiple Parents and Cross Reference links between notes.|
|BeSharp||Android||Simple and intuitive interface, free.|
|BeSharp for iOS||iOS||Simple and intuitive interface, incorporates Pomodoro technique and GTD/ZTD.|
|Vault 3 for Android||Android||Outliner for Android devices (Android 2.1 or later). Desktop versions are also available (Windows, Linux, and Mac OS X).|
|Zeptoliner||iOS||Outliner for iPhone and iPod Touch.|
|OmniOutliner for iPad||iOS||Port of OmniOutliner to iPad.|
|Outline Pro for iPad||iOS||Special outliner for writers and students. Ideal for papers, essays and speeches.|
Online outliners 
This table shows a list of online, browser-based outliners categorised by the functionality they provide (see 'Design' above).
|Name||Promote/ demote||Copy||Styling||Expose/ hide levels||Hoist||Search||Import OPML||Export OPML||Export other||Collaboration||Files|
|The Outliner of Giants||Yes||Yes||Yes||Yes||Yes||Yes||Yes||Yes||Yes||Yes||Yes|
See also 
- Code folding
- Folding editor
- Desktop Wiki
- Personal information manager, List of personal information managers
- Concept mapping
- Robert S. Houghton (2005-12-31). "Outlining Tutorial for Microsoft Word". Ceap.wcu.edu. Retrieved 2009-02-18.
- "How to create an outline in a document in a Word 2002". Support.microsoft.com. 2006-07-27. Retrieved 2009-02-18.
- "Overview of Windows Outliners". John.redmood.com. Retrieved 2009-02-18.
- As of 2013-04-09, thinklinkr.com website was non-functional, and with little activity or references elsewhere since 2011 the service is probably defunct.
|Look up outliner in Wiktionary, the free dictionary.|
- Comparison of desktop outliners
- Comparison of online outliners
- Overview of Windows outlining programs (at least 4 years old)
- Expanding Brain Outliner Wiki
- Outlines: The Do Everything Tool
- OutlinerSoftware.com, Discussion of Outliners
- An outline about outliners!, A collection of articles on the history, design and use of outliners