HyperLinked Text project is a Wiki-esque text file format and accompanying viewer.
HyperLinked Text (Hylt) is both a file format and a viewer for that format.
It uses (almost) flat text files to generate a Wiki-style database of hyperlinked pages, without either the complex markup of HTML or the esoteric database formats in which most Wikis store data.
It is geared towards users who desire a minimal interface between them and their data or like to store their data in formats which can be meaningfully stored in version control systems.
It was developed originally to match both of those goals, specifically for individuals writing fiction and wishing to track inter-character and inter-location relationships.