Metadata Search Engine
This is a bit technical, but interesting:
"In this article we describe the design and implementation of a full-featured metadata search engine within the Open Language Archives Community. ... Features include a variety of string matching algorithms; a thesaurus of alternate language names; language code searching; keyword-in-context display in search results; search for similarly spelled words; search for similar items; support for standard string search operators and domain-specific inline syntax; and automatically derived search links for other web search engines."