To be fair I had to look up the term because it's not used anywhere anymore. At least not anywhere I have worked.
The few profitable start ups I've had the pleasure to work for (including the current one I am at) heavily leverage confluence. A well structured confluence/runbook is indispensable in quickly ramping up engineers new to the company or handling common bugs/etc if you find yourself on call. There's never been a formal "process", but generally if you're doing something that is complicated enough that it can't be explained to someone in passing you make a new page and start writing. I personally do this by the seat of my pants. If I feel like the bus factor is high I will generally start writing stuff even if only I use it, so on the off chance I get hit by a bus there will be documentation somewhere about how to do things. But, I also religiously take notes for myself (ADHD is one hell of a drug) and I've found this alone a major contributor to making it to staff.
Confluence is just one solution though, I've also seen this done with a simple git repository and a well written front page README.md with URLs to various things, or having project specific knowledge in a special file along side the project README.md.