XMetaL
XMetaL, from
JustSystems (but originally developed by SoftQuad) is one of only two full-featured XML word-processors that offer authors an editing environment as close as possible to mainstream word-processors, but without trying to hide the structures that XML creates.
XMetaL was used to author all of the content on this website, and has been used and customised by Neil Bradley for various projects since 1989 (when it was known as Author/Editor).