[muydeemer]

As I see people mentioning Datalog-related software, I'm gonna throw a pebble into the yard as well - Graql (https://github.com/graknlabs/grakn) is a declarative graph-based query language with rule-based reasoning heavily inspired by Datalog and Logic Programming.

Disclaimer: I am one of the maintainers.

[muydeemer]

Just to add and clarify: it supports recursion (since a couple releases back) and pattern negation based on set difference (on current master branch, soon to be released).