X-Hive/DB is a powerful native XML database designed for software developers who require advanced XML data processing and storage functionality within their applications. The comprehensive X-Hive/DB Java API contains methods for storing, querying, retrieving, transforming, and publishing XML data. X-Hive/DB supports all major W3C standards, such as XQuery, XPath, DOM, XPointer, XML Schemas, and more.
Marko is a simple toolset that allows you to create markov chain databases of a corpus (or two) of text and then allows you to compare unknown texts to these databases. For any two marko databases you can calculate the probability that the unknown body is related to one over the other. Possible applications include intelligent mail filtering, plagiarism detection, and historical research.
Docco is a personal document retrieval tool based on Apache's Lucene indexing engine. It allows you to create an index for files on your file system which you can then search for keywords. It is not only a lot faster than searching by recursing through your file system every time, it also offers you extended query options like wildcards and fuzzy search as well as a visualization of result set intersections.
The Revisionist is a tool for extracting and indexing hidden metadata (such as deleted or modified text) from large collections of MS Word files. It can operate whole Web sites or SMB or NFS directories. It is handy for pen-testing, or it can be used just to spot embarrassing secrets.
Doodle is a desktop search engine for Linux. It searches your hard drive for files using pattern matching on meta-data. It extracts file-format specific meta-data using libextractor and builds a suffix tree to index the files. The index can then be searched rapidly. It is similar to locate, but can take advantage of information such as ID3 tags. It is possible to do full-text indexing using the appropriate libextractor plugins. It also supports using FAM to keep the database up-to-date.