There is at last PmWiki
http://www.pmwiki.org/wiki that has a concept of Wiki Trails:
http://www.pmwiki.org/wiki/PmWiki/WikiTrails. This are normal wiki pages with a hierarchical list that points to the pages you want to include in the trail. In addition to making this the basis for an ordered export, it can be used to create navigation elements on the included pages (next page, up, etc.) that depends on the current trail.
I have this in my idea collection for dokuwiki since I have read an article in the German computer magazine c't about a document preparation system:
Wiki-System als PDF-Generator (
Wiki-system as pdf generator) -- unfortunately there is only a german page for this document generation system:
http://www.virtuos.uni-osnabrueck.de/Produkte/Media2mult but the idea is really inspiring.