Each
WikiWikiClone seems to use its own markup language. There was another markup language, Setext, designed to work well with plain text. There was even a
PerlLanguage filter for it, so it was ready for use in wikis. It seemed well thought out.
--
AamodSane
Update, 2003: Work on setext seems to have stopped in the mid-1990s, and the format appears to be moribund. Most links to documents about it are broken.
See
StructuredText,
AlmostFreeText
CategoryTextFilter