Tockit is an open source project which was written by people from DSTC. It has a great interface that uses lattices called Docco. It's a representation of Lucene results combined with metadata extracted by plugins like POI. It seems to be only using the text found in documents, not actual concepts.
It helps to remove the empty nodes to better understand the results.
Screenshots are also available.
Other FCA tools written using Java are available at the ToscanaJ site.