The dungeon crawling role playing game, Legend of Grimrock, has just added Workshop integration to their game along with a new dungeon editor. This is all part of a free update to the game and available immediately.
The Public Beta testers have been very productive and have already created over 150 mods that you can subscribe to in the Grimrock Workshop
and start playing. Just find mods you'd like to add to your game and hit 'subscribe'. The mods will be available in the 'Custom Dungeon' section from the main menu of the game.
To get started with modding, the developers have put together a wiki here
with tutorials and resources.