We successfully adopted MediaWiki in our company and it was a really nice choice we made in early stage. We can easily search, tag pages, detect broken links etc.
I'll add another recommendation for MediaWiki. It is a good low-friction way to establish documentation for internal services and libraries. The markup syntax is rather idiosyncratic, but powerful enough for most of our needs. "Does it have a wiki page" is now a standard question for any new service or library in our shop.