SamIam is a comprehensive tool for modeling and reasoning with Bayesian networks, developed in Java by the Automated Reasoning Group of Professor Adnan Darwiche at UCLA. http://reasoning.cs.ucla.edu/samiam/
Robert Dodier's open source package for distributed, heterogeneous belief networks in Java - allows different conditional distributions http://riso.sourceforge.net
WEBWEAVR-III is a Java application that supports the construction of Bayesian networks, inference in standard and dynamic Bayesian networks and decomposable Markov networks, construction and verification of multiply-sectioned Bayesian networks (MSBNs), in http://snowhite.cis.uoguelph.ca/faculty_info/yxiang/ww3/
BAYDA software implements Bayesian predictive discriminant analysis, where the aim is to build a model for predicting the value of one discrete (class, group, category) variable using other variables. http://www.cs.Helsinki.FI/research/cosco/Projects/NONE/SW/
Open source package for the technical computing language R, developed by Aalborg University and Novo Nordisk A/S - analysis and structure learning of Bayesian networks with discrete and/or continuous variables http://www.math.auc.dk/novo/deal