Online Community Models?

buzzcutbuddha asks: "I have been tasked with creating/finding a Collaboration and Knowledge Management tool for work, and while there are some good commercial ones out there like Intraspect and Microsoft Sharepoint, but I want to look at it from another angle. Most people are aware of online community models like Slashdot, Kuro5hin.org, Everything2.org, it's Perlmonks derivative, and Wikki Wikki Web. Some may even remember SixDegrees from before it was retired. But are there any other notable online communities that have similar functions to the systems described above? I'm looking for a way to let people load documents or link to documents, discuss the documents, moderate the submissions and comments, and do searches. At this point, the underlying technology is not important."