To the point answer…, and no long paragraph, use MediaWiki with confidence, it can be downloaded for free and host your own wiki.
MediaWiki a custom made, open source wiki software platform written in PHP and built upon the MySQL database. It is licensed under GNU General Public License and it is used by all Wikimedia projects as well as many other wiki projects. Currently runs on dedicated clusters of Linux servers, with a few OpenSolaris machines for ZFS.
As I am using this product on SuSE Server and it works fine and smoothly.
Just for your information, if more than any person attempts to save a page, MediaWiki will attempt to merge their changes into the current version of the text and you will happy to know that the it is possible to merge changes manually in MediaWiki.
Happy to inform you!