Fun gameplay, positive, dynamic, on lisp

An android with a sword rebuilding a world -- how much better can it get? Some jump-challenges are quite hard, and their parts on the map are littered with places where I died, but everything feels alive and moving and stays challenging. It’s one of the gems out there, and the game engine is free software built in common lisp. I played the game on Steam, because back then it wasn’t available here yet, and enjoyed it a lot.