One of the best examples of collaborative documentation efforts at the time of writing is Wikipedia. This tool is built on MediaWiki, which provides a general purpose way of offering a wiki to those that want one. By default the system is fairly open, on the assumption that people using it will want to share and collaborate. There are more tightly controlled wiki environments more suited to the corporate world, where openness, sharing and collaboration cannot simply be assumed. Examples include Twiki and Confluence. All are good wiki offerings in their own way. Then, there's the Micro$oft way. Sharepoint is widely deployed in commercial development environments, supposedly to facilitate document sharing. Here is why using Sharepoint to do that is a very bad thing, why your project shouldn't do it and what to do if that mistake has already been made.

Sharepoint

Reasons to avoid Sharepoint:

It is only available for Micro$oft platforms.
It's expensive. It is a separately purchasable product (part of Office).
It's expensive. You need to run a portal server, which is also separately chargeable
It's hard to set up and administer. That's why there are jobs advertised for people with Sharepoint experience (see Sharepoint/Alfresco comparison) .
I have observed that people tend to be locked out of Sharepoint repositories far more often than is supposed to be the case. Sharepoint does not seem to be very good at, er, sharing.

See the links below. It's not just me that is against Sharepoint.

Links

Forums poststhat question the 'wisdom' of using Sharepoint when a wiki could be used instead.
An unemotional comparison between Sharepoint and Alfresco.
Sharepoint criticism from a Micro$oftie, dated July 2005.
An open discussion of the pros and cons of wikis versus Sharepoint.
'Sharepoint sucks' article(Feb 2008).
An article on how Micro$oft plan to use Sharepoint as another one solution with total integration as a lock-in strategy.

So, if you are not going to use Sharepoint, what do you use instead? Wikis are only part of the solution, since most wikis are not good at document management (they are better at the informal evolving documentation). Sharepoint is actually aimed more at official document management. A project is going to have a mixture of informal and formal documentation. Doesn't that mean that Sharepoint should be used as well as a wiki? No. I will give a detailed list on why not at some point soon, hopefully.