WackoWiki – Small, lightweight, handy, expandable, multilingual Wiki-engine. It's designed for speed and extensibility.
Includes a WYTIWYG editor, easy installer, many localizations, email notification on changes/comments, several cache levels, design themes (skins) support, template engine, URI router, HTML5 compliance, page rights (ACLs), page comments and is distributed under BSD-License. Also features RSS autodiscovery, file upload per page or global, multiple sites running of the same WackoWiki installation, clusters & relative addressing. Links can be CamelCase or freely formed links using an intuitive two-character markup. Compatible with PHP 7.2 / 8.0 and MariaDB / MySQL.
UI and admin pages remind me of Tiddlywiki.