Tools for Publishing in Multiple Formats?

Truist asks: "What are the best tools (windows or *nix) to use to publish a single source document in multiple formats, specifically plain text, multi-page HTML, and PDF? I'm trying to publish a (60-page+) NetBSD installation guide/documentary online, and I want plain text for easy download and 'less'-ability, HTML for easy browsing and search engine indexing, and PDF or Postscript for easy printing. It's currently a Word document (I know, I know - I'm happy to manually convert it to something else) with multiple styles, including regular text, lists, internal links, external (web url) links, code, and notes, and I'd like to preserve as much as possible of each in the final output. Some additional notes: there are no graphics, and I expect to update this document periodically, or to split it into parts and maintain the parts (think master document / subdocuments). It won't be updated too often, but if re-publishing could be scriptable, that would be fantastic."