HLM: Hierarchical Linear and Nonlinear Modeling by Scientific Software International, Inc. 
Software for hierarchical linear modeling. Free student version available (with restrictions).
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Interaction by Daniel S. Soper
Free Windows software program to draw and analyze statistical interactions.
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OpenEpi by Dean AG, Sullivan KM, and Soe MM | Emory University 
Free, open source software for epidemiologic statistics.
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PASS: Power Analysis and Sample Size by NCSS Statistical Software 
Software to perform power and sample size calculations. License required.
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PS: Power and Sample Size Calculation by Dupont WD, and Plummer WD | Vanderbilt University 
Software to perform power and sample size calculations. Free to download.
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WesVar by Westat 
Replication-based variance estimation for analysis of complex survey data. Import/export various file formats. Registration required.