BookStack is a free and open-source wiki software aimed for a simple, self-hosted, and easy-to-use platform. Based on Laravel, a PHP framework, BookStack is released under the MIT License. It uses the ideas of books to organise pages and store information. BookStack is multilingual and available in over thirty languages.
such a useful piece of software. 5/5 blocks because you can self-host and use it without having to trade something in return (https://www.bookstackapp.com/docs/admin/installation/).