Double Tree is a free, open source Java application providing a visualization component for supporting exploratory corpus analysis. It focuses particularly on analyzing concordances, and can also represent a KWIC for a single word by collapsing the contexts into a double sided tree. Each side of the tree can be expanded independently to browse the results.
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The website for EURAC's LInfoVis project, which produced Double Tree, currently returnes a 401 error for the project's tools and information. The project about page is still active, however, and may be viewed at http://www.eurac.edu/en/research/projects/Pages/projectdetails.aspx?pid=6109&depId=11&pmode=1
The tool is no longer available
The links have been fixed (although, they all point to the general homepage. the tool is not available anymore but general information is).