I used to use phpwiki for a personal, behind-the-firewall wiki. It was simple, though it was many files, and gentoo packaged it. Then, there was a version upgrade that required a database and lost all my (handful of) content. I switched to pwyky because it was a single file, simple, and SBP wrote it. But its syntax doesn’t support nested lists, and it’s not reStructuredText.
rstiki is a minimalist single-file CGI wiki, in python, which uses docutils to render reStructuredText markup.