LATtice is a free visualization tool for exploring and comparing texts across corpora. It also has features for 'drilling down' to determine what rhetorical categories make texts similar or different, and shows multiple visualizations in the same view. Documentation is available with download, and LATtice is available in Windows, OS X and Linux versions.
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LATtice also appears in Project Bamboo's DiRT, a registry of digital tools suitable for academic research. DiRT contains a wide range of tools and software searchable by task, such as annotation, content management, collaborative research, or authoring. It is an excellent resource for Digital Humanists seeking the right tool for the task at hand.
View LATtice in DiRT:
http://dirt.projectbamboo.org/resources/lattice
View the full site:
http://dirt.projectbamboo.org/