Static Wiki is a pure HTML Markdown-based wiki which can be read without additional software, and even while offline.
You're looking at it right now!
You can find a markdown sample page here.
Static Wiki's sources for creating the HTML pages are regular Markdown text files. You can use them anywhere else and they will work the same way.
You can also make backups more easily. Want to use
.zip files? Git repositories? Post directly to the web?
The web files generated use a base theme that shouldn't require any online resources to display properly, so you can take your files with you and present them to friends or work on your things without requiring an internet connection.
Did I mention it'll look an awful lot better than just a plain text file?