Nothing much anymore. Wikia disabled i, as have Wikipedia. Heck, even mediawiki.org don't have it enabled. There are some wikis out there that do, though, and it simply allows you so search for your content by MIME type. So if you wanted to find all the .ogg files or .jpg or .png or whatever, you would use this tool.
I have to ask one more question about MIME. MIME is the same as Multipurpose Internet Mail Extensions or it is different in this term. Just asked out of curiosity and nothing offensive. Thanks for your great helpful knowledge.