[kherud]

Answer Set Programming is an incredibly powerful tool to declaratively solve combinatorial problems. Clingo is one of the best open source implementations in my opinion: https://github.com/potassco/clingo

  - Based on conflict driven nogood learning, it has incredible performance (including good multithreading)
  - It has different optimization and enumeration modes
  - It has strong built-in heuristics, but also allows manual heuristics
  - It allows incremental solving
  - It has a nice API to integrate other solving paradigms (like difference logic and constraint programming, for which implementations already exist)
  - There is a huge ecosystem around it

And much more, go check it out!