This is a somewhat broader question about a topic I think every organization/business is running into once there's more than one DevOps person: How to keep and curate organizational operations knowledge so that it remains up-to-date, easily accessible, and is useful to newcomers?
The goal of this question is to collect a sample of solutions for people to choose from. My business/organization hasn't (yet) found a good way of dealing with this issue.
Definition: Operational Knowledge -- That what is needed to know to get things done, keep the infrastructure running, and up-to-date.
Some Examples: What AWS regions is our main RDS cluster in? Where and how do we store our secrets? What's the loadbalancing setup for our web page? What is our role/user structure in Postgres? How is the VPN setup and what's needed to add a new user (generate certs etc.)? What are the steps to deploy a new version of code XYZ to production?
How does your organization handle this? Do you run your own wiki (which one?), Github's wiki, Google docs, Evernote, markdown files in a git repo, Word docs (?!?) on a central server, or what else?