Originally devised by ZopeApplicationServer's creators for easy documentation, it found its way into ZwiKi as one of its markup languages. It is remotely similar to WikiWikiWeb's TextFormattingRules although it has several key differences.
[I expect some kind of structured text to become a very popular publishing format in the future. If wikis become mainstream, most people will have some intuition about editing structured text; and structured text really is easier to write and more structured than, say, WYSIWYG documents.
Probably the biggest disadvantage currently in most structured text formats is the obsession of coming up with some specific syntax for everything: different kinds of links, images, tables, etc. ad nauseum. Most of these don't have intuitive markup.
There are some new projects that try to make general purpose structured text formats, like ReStructuredText, AlmostFreeText, a software package called APT (http://www.xmlmind.com/aptconvert.html) and my own stx2any software (http://sange.fi/~atehwa/Stx).
It is surprisingly hard to make structured text rules that don't irritate people in some way. The markup should be intuitive, pretty, traditional and not get in your way. You should be able to escape into direct markup (for example in HTML) when you really need to. The result of the formatting should be very simple, not to second-guess other people's personal preferences. And it would be nice for the format to be extensible... ReStructuredText is quite well thought out, but it still has a few questionable choices, such as the use of backticks for literal formatting. StructuredText (the Zope thing) has sectioning by indentation, which irritates many. APT has <> as emphasis syntax, wiki has apostrophes, everybody has obscure syntax for complicated things like tables, and I guess somebody will be irritated by my choice of heading markup (lines beginning with exclamation points). -- PanuKalliokoski]