Ask HN: How do you document your processes?

Working for a large enterprise I find some attempt at process documentation is often made when new projects are running, which over time goes stale / lives with the project rather than being updated with the business/processes. There's no cohesive view of the organisation whereby you can drill down into the detail of each piece.

Do you work for an enterprise, a startup, or something in between? How are your processes documented; are they across the business, or maintained in silos? What tools do you use to aid in documenting and maintaining these?