I'm currently migrating my worldbuilding and conlanging project to Dokuwiki. Right now I have an Obsidian vault used for brainstorming and drafting and a public Mediawiki for stuff I feel is worth showing off. Like Obsidian, DW stores everything as plaintext (it's not markdown but it's readable and the tables are better IMO). Like Mediawiki, DW keeps a version history so I can keep track of how my ideas evolve over time, which is crucial for conlang documentation. I keep tons of example texts that may reflect earlier phases of the grammar and vocab that I may need to reference. Unlike both Obsidian and MW, Dokuwiki has access control, so I can keep a private namespace for drafts and a public namespace for stuff I think is polished enough to show.
I'm not sure DW meet's OP's requirements for "out of the box" functionality though. I think it's intended to be rather bare bones but be very easy to extend with plugins. The plugin browser is built in, so customization is a breeze. Plugins can be individually installed, enabled, disabled, and updated through the admin GUI.
Otter's almost there. It needs a few things before I'd call it a wiki rather than just a documentation system, namely backlinks and a way to differentiate between links to existing and nonexisting pages, as well as a way to see what nonexisting pages are most wanted.