What knowledge base application do you use?

For our startup, we've been looking at different options. Best one we've found so far seems to be KBPublisher (but it does cost):

http://www.kbpublisher.com/

Before I pull out the credit card, wanted to see which ones people here use. I'd like one that we can ideally host ourselves (not required, tho), that has a good wisywig editor and other non-developer members of our team can use easily (so good UI).

This application is for our company's internal use only.