There are dozens of good open-source wikis available. Getting one set up is generally less than an hour's work.

Getting people to contribute can be a problem, but if the workflow is easy and there are things to document, it will work out.

Cleaning up after the fact is usually a bigger problem. Even with full-text search (a requirement, IMO) a large wiki can become a terrible dump. Library science is a real field, and if you can afford a librarian, you definitely want one.