mediawiki

MediaWiki is the software that runs Wikipedia, and you can run it yourself. It is a mature, extensible wiki platform: collaborative editing with full page history, templates, over 350 languages, and a deep extension ecosystem. If you want a knowledge base or internal wiki that scales to hundreds of millions of readers and has two decades of hardening behind it, this is the proven answer. GPL licensed and free.

Self-hosting is a classic LAMP-style setup: PHP, a database (MySQL or MariaDB), and a web server. Getting a basic wiki up is genuinely simple, and it runs on modest hardware. The work comes later, with extensions, spam control, upgrades, and scaling, which is real but well-trodden ground with enormous community documentation.

For a team or community that needs a serious collaborative wiki, MediaWiki is free, battle-tested, and hard to outgrow. Solo users often find it heavier than a personal notes tool warrants; it shines with many editors, not one. Larger organizations get the most out of it, and there are hosted providers if you would rather not run PHP yourself.

The catch is that MediaWiki feels like what it is: enterprise wiki software built for Wikipedia's needs, not a slick modern docs tool. The editing experience and default look are dated next to Notion or a static docs site, and making it pretty takes skinning and extension work. Choose it for durability, scale, and openness, not for out-of-the-box polish.