If you're just looking for a private FAQ/Knowledge Base, you could use this: https://helpjuice.com
Or use HelpScout's Docs feature and just ignore the ticketing system and make the Doc's URL private/password protected: http://www.helpscout.net/features/docs/
The mostly-free way to do this would be using something like Google Docs (shared within the company) or setup your own internal company wiki.
Two basic ways to go: