The Fellowship of the Things
The dwarves were making it for the city of Tos to help defend the borders. The Ruby was the largest one ever found and said to have been cultivated in an umber hulk nest. Tales say that it was part of a cannon of some kind that could pierce almost any surface. No one is really sure how it worked as the plans to construct it were taken as well as the pieces of the cannon on its way to Tos. Blessed by Moradin.
(What the party has learned) The ruby cannon is actually a sentient being made from gears and various materials. The ruby itself seems to be a focal point for a laser. It isn’t 100% clear but it seems that the mind of its creator might be inside it. Who it is is unclear, though it seems to know it’s general purpose is to defend the city of Tos. It was last seen in the possession of Duke Krailor who promised to have it protected and used purely on a “absolutely needed” policy.