single binary install, and if you already have md files you just point it at them and go... if you don't like it (even after you edited a few of your files with it), well your files are still there, still in markdown
I want to second Dokuwiki. It is a step up from text files in a folder, easier to install and maintain than Jekyll (I am a big fan of Jekyll but have a deep-seated hate for Ruby). When compared to all the other wikis it is by far the easiest to install, maintain, and move to another server.
Dokuwiki is all text files and a version of markdown, the files can easily move to another markdown system.