Blasted Fortress is a physics-based castle assault game with an added layer of resource management. Even while you're not playing, crops grow, market prices fluctuate, seasons change, and you may come back later to be greeted by disasters that happened while you were away or gifts to bolster your resources. It's a blend of physics decimation, looting, hoarding, and RPG-style enhancements. If you're more creatively inclined and want to add more content to the game, you can even create your own buildings to siege using the built-in building editor.
This is a screenshot of the Blasted Fortress beta which a handful of people took part in around mid 2013. The game has improved its looks a lot since.