Souffle Datalog is used for defining program analyses in such projects like Doop [1] for Java and cclyzer++ [2] for LLVM.
GitHub's CodeQL [3] is another Datalog dialect used for detecting bugs and vulnerabilities.
Datomic [4] is a database that uses Datalog as the query language.
[1] https://bitbucket.org/yanniss/doop/src/master/
[2] https://github.com/GaloisInc/cclyzerpp