People might not be aware that the JVM (Java Virtual Machine) specification includes a class verifier written in Prolog, see http://docs.oracle.com/javase/specs/jvms/se7/jvms7.pdf
Clementine -- a data mining application purchased by SPSS
SPARK toolset -- a rigorously defined Ada subset used for developing software correct by construction. This approach is used in areas like aviation, transportation, medicine, energy, etc. where failure is not an option.
ECLIPSE-CLP -- an open source constraint logic programming library used to solve various resource allocation problems. Think of it as a poor man's Operation Research expert.
Experian, the credit rating company, bought out Colmerauer's Prologia company: http://www.experianplc.com/news/company-news/2005/25-10-2005...
ContractExpress/DealBuilder from Business Integrity Ltd http://www.business-integrity.com/
InFlow from OrgNet http://www.orgnet.com/
GridMind tool - a for modelling and simulation new technologies implementation into energy grids (smart grids, smart metering etc.). They have to generate detailed complex models satisfying lot of rules which to make models realistic. Prolog together with CLP is excellent tool for that. Fast development, small code, elegant solutions. www.mycroftmind.com
David Warren (Leading Professor at Stony Brook University): "We at XSB, Inc. use Prolog and Java. We use Prolog for knowledge extraction and standardization and for ontology representation. We have (to me, somewhat surprisingly) found that our Prolog code is more stable and we spend less on maintaining it than we do our Java code. It may be programmer skills, but I think it is also due to the much more succinct expression of similar functionality."
The Nokia N900 phone used prolog to do ui state management .... prolog in a smartphone!
London-based startup Texrazor performs text analysis via API and the engine behind it is coded in Prolog http://www.textrazor.com/technology
Prolog does social and organizational network analysis for clients around the world. http://orgnet.com/inflow3.html
Orgnet, LLC also uses LPA Prolog to do data analysis, especially for hidden relationships and patterns in business data... for examples, see: http://thenetworkthinkers.com
etc., see the discussion on LinkedIn