Knowledge forum software / Software for internal use

I’m looking for a knowledge forum software/website which could be used, internally, to keep track of and share various bits of knowledge/production support. It will be installed somewhere on the development / testing servers and preferable should be on SQL DB, and open source with source code.

Do you have any suggestions / recommendations?

SharePoint?

It is not free, but you might want to take a look at Atlassian's Confluence Software

Thanks JamesK, I will be sure to take a look.

Looking for something other than SharePoint. More of a forum type UI.

We use a Wiki - but it aint a "forum type UI". Main benefit for us is that anyone can edit any page, there is a history of the page's previous content, and folk can add a new "page" (simply by defining a valid LINK to a new, non-existent, page and then clicking on the link and filling in the "create a new page" form that is displayed.

The WIki formatting is a PITA IMHO, but its "okay". Given my lot are all techies, rather than technophobes!, I'd prefer to write the content in pure HTML. Tables, for example, are a major PITA to write in the Wiki, so if I was doing it again I'd choose a WIki that allowed pure-HTML code for the content. Or a WYSIWYG editor.

Thank you Kristen. I will be sure to take a look.