Maybe you've seen this already, there is now a
official Irrlicht Engine Wiki available on irrlicht3d.org. Feel free to edit and add content there, the only thing you need is a password which is written on the front page of the wiki. If someone would have the time to reproduce the content of the
old irrlicht wiki from the webarchive there for example, it would be great. I will also try to add some more useful articles on there soon.

The wiki software I've installed there is
PmWiki, although with the skin I used on the page it may look like
MediaWiki, the software behind the Wikipedia. I first thought about using Wikipedias software, but after some evaluation, there are several advantages of PmWiki over Mediawiki. One of he biggest advantage for me is that PmWiki stores its data directly on the file system and does not need a database backend, making installation, backups and hacking very easy. And although it doesn't look very stylish with it's default skin, PmWiki also is a very mighty piece of software with tons of configuration possibilities, plugins, skins, documentation pages and hundreds of users. Especially with more than 100 plugins available for PmWiki, you can do almost everything you need. So I can really recommend this software.
If you want to set up your own wiki, there is a
comprehensive comparison of wiki software available at wikipedia.