A while ago I finally finished some work on the wiki for the UnrealAdmin page. It's an modified version of the MediaWiki wiki engine (the same one as is used for WikiPedia). One of the more important things I modified was to hook up the user system with our main site that was powered by vBulletin. It's isn't as easy as it looks. Because MediaWiki is quite limited in the username format, only alphanum and _ are allowed. But vBulletin allows pretty much everything. This create a very annoying problem. How to hook up those users. I could imply convert the username to MediaWiki style, but this could create name clashing. So instead I ripped out the whole User namespace support and changed the way usernames where parsed. Username will now foward to the vBulletin profile page for users that exist. Some of the changes required modifing original files (which I don't like). So right now when a user type ~~~ (for a signature) it will be replace with a new tag [[profile:uid|Username]]. The username is ignored in further processing, it's only useful when editing a page and still being able to see the actual username. All links to the user namespace, [[user:Username]], will also be rewritten to an url to the vBulletin profile page (if the username can be found). Now this creates another problem, some usernames can contain characters so that [[user:Username]] doesn't work well. I fixed this by adding some magic: [[User:?|Username]] will work for these usernames and still allow me to look up the actual info.
If you are creating a new site with MediaWiki (or any other wiki) and vBulletin simply limit the characters that people can use to alphanum and the underscore (or space). This will save you a lot of work.
Besides the vbulletin integration I also made a couple of other extentions, pretty much all are available. While working on extentions I found out that MediaWiki doesn't really make it easy to develop extentions. Sometimes you need to change stuff deep inside some routines, or at least on certain places. Then you'll find out there are not enough hooks available to get to the right place. vBulletin 3.5 did it much better. For example simple things as adding ACL for pages isn't possible without modifyin the original code. But then again, MediaWiki is one of the nicer PHP powered wikis I've found so far, and their text syntax is nice too (much like the syntax UnrealWiki uses).