A simple wiki which supports Markdown syntax?
applicative: Gitit rules; I don't know if it counts as simple, and it certainly doesn't count as "written in PHP/Python/Ruby/Java" -- are you sure you need that?:"Gitit (http://gitit.net) is a wiki backed by a git or darcs filestore. Pages and uploaded files can be modified either directly via the VCS’s command-line tools or through the wiki’s web interface. Pandoc is used for markup processing, so pages may be written in (extended) markdown, reStructuredText, LaTeX, HTML, or literate Haskell, and exported in ten different formats, including LaTeX, ConTeXt, DocBook, RTF, OpenOffice ODT, and MediaWiki markup."