Doug Engelbart developed the first outliner in the 1960s as part of the Augment system. Later, in the 1980s, several widely adopted outliners for personal computers were developed by Living Videotext. Outlining was used to build Frontier in 1992. It featured outliners in its text, menu, script editors, and object database browser.
XML 1.0 was released in 1998, based on the recommendation of the World Wide Web Consortium (W3C). In 2000, OPML was developed with Radio UserLand, an outliner with the OPML native file format, released in 2001.