BookStack

BookStack is a simple, self-hosted wiki platform that organizes content into Books, Chapters, and Pages (like a library). It features a straightforward WYSIWYG editor and search. It's easy to set up and use, making it great for small teams or communities wanting a clean, structured internal documentation site. It's free and open-source.

It scores for its intuitive, book-based metaphor that lowers the barrier to creating organized, hierarchical documentation without complex features.