MediaWiki

We've recently installed MediaWiki to set up a nice knowledge base for our internal use (for ITerating project). It's a powerful engine and it works great for keeping in one place specs, proposals, discussions on new ideas and features.

The Upload Image interface could have been placed better as it is difficult to add new images while editing. Also, something that I find funny, although it allows different files to be uploaded, they're all under the tag "Image".

One more thing I have to say, its PHP class structure and code are just beautiful !!

MediaWiki powers wikipedia, which has helped establish it as the leading wiki platform.
Mediawiki has definitely proven its realiability and scalability. Yes, it could be much easier to use, and much easier to customize. It seems that the development efforts are focused on supporting wikipedia, now you average user in search of a great wiki.

This is definitely the best wiki around but although initial setup is intuitive skinning MediaWiki is not. Documentation is lacking in some areas. If you have experience with wikis, this is the one to go for. For new users though, set up is a challenge. Take care when reading the help and tips as many of these are out of date.

MediaWiki is an amazing piece of software, it's open source, stable, powerful and very very useful. I always got great support over the mailing lists or IRC channel. It has so many features yet it's so easy to customize. What could one expect since Wikipedia uses it for such a long time? I wouldn't recommend it to an amateur though since it wasn't designed for small setups.
Still, there are a couple of items on my features wish list, like a simpler WYSIWYG editor or the possibility to use your own skins.

Yes ... pretty much it's what it is. After trying a bunch of wiki implementations, I went for MediaWiki and never looked back :)