Is there good open source project that apply semantic web, modal logics, and similar technologies Recently such themes as semantic web, modal logics, business rules have seen increased interest as research topics in computer science (alhough many of then have more than 80 years of history), but are there any open source projects (even better if they are actively used in commercial applications as well) that use these technologies and where one can participate and get new challenges for research?

I have found a lot of research projects (e.g. satisfiability solvers, logic programming environments) but at present I don't know many succesfull applied applications. There have been few reports on some of them in the jornal of "Theory and Practice of Logic Programming" - mostly about solving scheduling problems with logic programming methods. But maybe there is some open source projects as well?

Sometimes it seems to me that modal logics (semantic web is part of them) and logic programming gives false impression about their power and their generality has few applications, e.g. the concrete algorithms of integer programming or scheduling are more powerfull and ready for applications than general methods suggested by the former ones.
Not open source, but the AI engines of some successful computer games are based on modal logic, see e.g. "Using Exclusion Logic to Model Social Practices" and "Introducing Exclusion Logic as a Deontic Logic"  by Richard Evans.