The basic idea behind StructuredText is to avoid the necessity for a markup language like TeX, Troff or HTML/SGML/XML and being able to create richly structured documents without thinking about the markup. The StructuredText markup language is intiutive, minimal and unobtrusive.
There are several different versions of StructuredText:
[http://dev.zope.org/Members/jim/StructuredTextWiki/StructuredTextNG StructuredTextNG]
One application of StructuredText which is currently discussed on the DocSig is the generation of documentation from Python DocStrings.