[open-source] Anybody knows any knowledge base open source?

In addition to MediaWiki that was mentioned by Kenny, you might also look at MoinMoin.

Choosing between MediaWiki and MoinMoin can be a bit tough. Here are some points to consider:

MediaWiki

Pros:

  • Made for wikipedia, thus is very mature and scalable.
  • Fairly easy to set up.

    Cons:

  • Made soley for wikipedia. Thus it can be a bit of a pain to customize how you like it.

MoinMoin

Pros:

  • Very mature software.
  • Huge amount of plugins and third party modules available.

    Cons:

  • Can be a pain to install.

There are a huge amount of other wikis available, but those are the main two I would consider.