I've released version 0.1 of DownMarker, a small desktop application that can be used to to view, navigate and edit a set of interlinked markdown files:
In case you don't know Markdown, it is a "easy-to-read, easy-to-write plain text format" intended to be converted to HTML. I first encountered it as the format used at Stackoverflow for editing questions and answers. In fact, DownMarker is based on MarkdownSharp, a library generously released as open source by the stackoverflow team.
Currently some things are still missing, but my hope is that DownMarker will work well for creating light-weight wikis inside your version controlled projects, or anything else that can store files. Let me know if you find it useful!