My team hosts a meeting every two weeks to talk about staffing - who's overworked and why. We also discuss what problems we're dealing with and solutions we've found for those problems...so the group's knowledge grows, but not in an official, legible way. It's still tribal knowledge, but an effort is made to at least increase the size of the tribe.

The only time when people are absolutely required to document something is when it's a deliverable to a customer...so the customer needs to understand the product we're delivering to them.

We're all supposed to be using an engineering notebook to help document designs...but those really only come into play when someone leaves the company and the company is trying to retain as much IP as possible. Though they are incredible useful on an individual level.

Other than that, it really comes to down to finding time to draw a diagram or do a brain dump into a document describing how something works. Maintaining ICDs (Interface Control Documents) describing software/command protocols or hardware interfaces is pretty easy and provides a lot of information.