A while ago, somebody has created a list of outliner software. it was posted into the outliner forum in the year 2008 and the list is really long. Large scale software projects like asksam, myinfo and Onenote were mentioned. But some more recent projects like Obsidian and Citavi are missing. Also some smaller Open source projects like Cherrytree are not in the list yet.
But let us slow down the situation a bit and start from the beginning. The perhaps most popular outliner like software from the 1980s was Asksam which was an MS DOS application. The idea behind asksam was to create a full text database on the local floppy drive and then do a full text search in the database. This concept was new in the 1980 because it was the first time that larger amount of data were searchable.
In the 1990s more outliner programs were created notable IBM Lotus notes. The asksam project was stopped and the possible alternative is myinfo. In addition, lots of shareware and opensource outliner programs were created. The sstate of the software is working with a two pane window which allows similar to asksam to retrieve the database in fulltext.
The reason why so many different programs are available which are of course completely incompatible to each other is because the concept of an outliner software makes sense for many PC users. It seems, that each of the 3 billion computer users in the world has a need for an individual outliner tool.
Some popular projects in the recent years are Microsoft onenote and Obsidian. Similar to the first outliner software in the 1980s the idea is to structure knowledge in a database. Another popular software which is used mostly by programmers is the Emacs org-mode which is some sort of outliner for the emacs editor.
Let us try to investigate the subject in detail. There is a difference between a programmer IDE like eclipse and an outliner software like myinfo. The average outliner is able to edit many files at the same time. In a text editor, the user opens a single file and makes some changes. While in an outliner program, hundreds of files are opened in parallel in the left pane. In addition, the average outliner supports images and attachments. In contrast, a text editor used for programming software isn't doing so.
Perhaps it makes sense to take a closer look at the myinfo project, because it is a mature outliner software which includes all the important features. The main feature of the software is, that it can be used to create a structured text document. In the left pane, the user sees the outline which is the table of content of the text while the right pane shows the content. The text contains of prose text, bullet lists and very important images and tables. In addition, the user can do a full text search in the content so that he can find older entries easily. This is – in short – the basic principle of an outliner software.
The Obsidian software has modified the principle a bit. Obsidian is a graphical mind map editor. The standard layout is different from a word processor, but Obsidian shows a graph of connected nodes. The ability to link from one entry to another is very important.
What we can say for sure is, that the amount of outliner software will grow in the future. It seems, that there is a need to program different sort of software. A single tool which is used as the default outliner is not available. Even the large Microsoft Onenote software wasn't able yet to reach a larger audience.
A very interesting but seldom mentioned software is AZZ cardfile. The dominant difference to other outliner programs is, that AZZ cardfile doesn't support nested cards. There is no ability to create folders and populate them with subfolders, but all the cards are on the same level. This principle emulates a classical paper based notebox and it is different from a directory structure used in computing. The AZZ cardfile software was created as an improved cardfile.exe software which was preinstalled in the Win3.1 software. cardfile.exe was a very basic index card software.
Timeline
Freebyte Treepad, 1995-2019
Notecase Pro 2011-today
Notecase 2005-2008
AZZ cardfile 2001-today
asksam 1985-2008
Inforapid 1997-today
Onenote 2003-today
The majority of the programs were created from year 2000 until today. Software projects like Inforapid, Treepad were programmed mostly for the Windows operating system. Older examples for outliners like Grandview and Asksam were available in the 1980s for MS-DOS PC but they were never very popular or powerful. The interesting situation is, that most projects are promising to reinvent the idea. The user is explained what a personal knowledge system is about. But from a technical side all the programs are working with the same two pane outliner principle. In the left pane the outline is shown while in the right window the full text gets entered. Even more recent projects which are programmed from scratch are working with this principle.
The perhaps most dominant concern for the end user is, that the file format is not compatible to other programs and if the software is no longer maintained the user can't switch to a newer program.
References
[1] List of outliner software https://www.outlinersoftware.com/topics/viewt/807