geoLucene is an extension of Lucene that allows to effectively index and search documents that contain locational information (longitude/latitude). It uses R-tree as a spacial index. See http://www.gossamer-threads.com/lists/lucene/java-dev/53378.
Roosster.org is a personal "on-demand" search engine. This means, it indexes only items/entries/files/URLs you explicitly tell it to index and provides a full-text-search over indexed items.
Goto http://roosster.org/dev for all details.