[amq]

I was looking into open source knowledge / wiki base solutions recently, and I found https://www.getoutline.com/ to be the most usable.

[Vaslo]

10 bucks a month though...

[vladvasiliu]

For the hosted version.

You can host your own for free: https://github.com/outline/outline

[FalconSensei]

then you have to pay your host