Knowledge management for few bucks. Any

I’m involved in designing a web portal that is going, among other things, to help their users to share knowledge for IT Topics submiting very technical documents. Does anyone knows about some tools that ease the development of a simple knowledge management application to be embedded in this portal? Because this “Knowledge sharing” is not the core business of our customer I’d like to avoid big development efforts for this part of the project.
Automatic taxonomy is a requirement.
Thanks in advance for your help.