Parser working with XML in Apache Xerces family. It has a framework to build components for the parser and modular settings easy to program. Available under the Apache Software License.
Z39.50-1995 Prototype Indexing and Search Engines. Deals with documents and questions like lists of words and as response is given a list of documents ordered or ranked by their statistical similarity to the query. Supports for improving the question using relevance feedback. It is in the public domain, freely available