Apache Lucene, have you used it?
Probably the most used web search engine
Created by Doug_Cutting, who is in cloudera now, Lucene has become one of most used web index and search tools. There are over hundred of open source projects using Luence. It is easy to be confused, Lucene is not a single projects. It has several sub-projects.
1. Apache Lucene, based on JAVA high-performance, full-featured text search engine
2. Apache Droids, create and extend web robot
3. Lucene.Net, Luence for C# .net framework
4. Apache Lucy, work with C, Perl, and Ruby
5. Mahout, scable machine learning. It is to say after searching the documents, learn and conclude something from the documents.
6. Open Relevance Project (ORP), for Machine Learning and Natural Language Processing
7. Pylucene, a Python extension for accessing Java Lucene
8. Solr, very popular full text search tool based on JAVA, using Luence engine.
Not a very pretty logo, Lucene might need to consider of the re-design