alt Hacker NewsProfessional tech writer here: We use GitHub and a tool called OxygenXML to write docs-as-code in an XML DTD called "DITA". It's a hefty IBM invention from the early aughts, but it covers every use case I've thrown at it, from small documentation sets to multi-thousand-page monsters. Supports PDF, HTML, Word, and many other output types.
DITA's so great at everything _except contributions from non-tech writers_ that half of my career has involved migrating tech writing stacks that use it to Markdown/SSGs in git repos.
DITA's benefits require a certain scale that most tech companies never achieve. And the Open Toolkit is a nightmare piece of software.