Most people know about MediaWiki even if they don't realize they do, because it powers Wikipedia, but I wish more people used it for documentation.
You can create highly specialized templates in Lua, and there's a RDBMS extension called Cargo that gives you some limited SQL ability too. With these tools you can build basically an entirely custom CMS on top of the base MW software, while retaining everything that's great about MW (easy page history, anyone can start editing including with a WYSIWYG editor, really fine-grained permissions control across user groups, a fantastic API for automated edits).
It doesn't have the range of plugins to external services the way something like Confluence has, but you can host it yourself and have a great platform for documentation.
You can create highly specialized templates in Lua, and there's a RDBMS extension called Cargo that gives you some limited SQL ability too. With these tools you can build basically an entirely custom CMS on top of the base MW software, while retaining everything that's great about MW (easy page history, anyone can start editing including with a WYSIWYG editor, really fine-grained permissions control across user groups, a fantastic API for automated edits).
It doesn't have the range of plugins to external services the way something like Confluence has, but you can host it yourself and have a great platform for documentation.