Ask HN: How to encourage and maintain a long term organizational knowledge base?

We, as many others, use Slack to communicate. But this only works well for real time and short term projects. Those teams that do document stuff for the long term, either does it poorly (structural, and does not maintain it) or uses different services (Google Drive, Quip, Dropbox, different wikis, etc) more suited to their needs. I'm both talking about high level technical documentation and organizational documentation. This makes it hard do on-board new people, hard to get to know other parts of your organization and hard to search for answers without bothering others. I really want to hear from you what success stories you have growing a documentation oriented culture and what others can do to encourage the behavior.