Many universities have produced Bayesian network software. B nets are used in the software of giant companies like Google, Microsoft, IBM, Oracle, Autonomy (now part of HP), SAP, SAS, ... But how about smaller companies? This is a list of smaller companies that make a living almost exclusively from selling B net software and services
Other companies that I've heard mentioned but no longer seem to be active, or at least don't have an easy to find website, are:
(last updated, Jan, 2015)