User:CliffordD
Note Note: If only logged-in users are allowed to view pages, make sure you add the request account page to $wgWhitelistRead. For example: $wgWhitelistRead = array('Special:RequestAccount','Main Page');
In other languages you have to replace "Special" and "Main Page" with the words that are used instead of special in your language like "Spezial" and "Hauptseite" in a German wiki, otherwise nobody will be able to create an account.
To further categorize users based on their interests, you can set up MediaWiki:Requestaccount-areas. This should be in a format like:
*Topic|Topic wiki page|text to append to all interested users' bios |text to append to all interested users' bios in group0|text to append to all interested users' bios group1|text to append to all interested users' bios in group2|...
These group numbers are based on $wgAccountRequestTypes. So if 0 is the index for 'authors', then 'authors' interested in a topic will have the group0 text appended to their biography. This can be useful, say, if users can be approved as either authors or editors. Authors can have "category:X authors" where X is a topic, like "mathematics", and editors can have "category:x editors". You can have as many groups as you want, but you need at least one.