This CMS does not make use of a database since it relies on plain files.PmWiki is a wiki-based system for collaborative creation and maintenance of websites.
PmWiki pages look and act like normal web pages, except they have an "Edit" link that makes it easy to modify existing pages and add new pages into the website, using basic editing rules. You do not need to know or use any HTML or CSS. Page editing can be left open to the public or restricted to small groups of authors.
It is also possible to let the wiki run without a preexisting webserver installation, as stated in http://www.pmwiki.org/wiki/Cookbook/Standalone : a minimal webserver written in PHP is available, which can do the job.
Since the server itself uses relative path names and does not need installation, IMHO the whole wiki (server+content) is portable.
The few Megabytes needed to let the Wiki run helps in making it portable too.
I unpacked the wiki pages and the server files into a couple of folders, I did the few required setup steps and... a double click.
Hope you will like it.