Legend of Grimrock's map editor has been taunting us for some time now, with developer Almost Human posting videos like this. Well, lucky for us, the map editor is now available to everyone who owns the game through Steam. According to their blog post, this is because Steam's automatic update feature is the best and easiest way to distribute the map editor along with any and all updates to it.
In order to get the map editor beta, just right click on the game in Steam, enter properties, and opt into the beta.
Also important is the advent of Grimrock Nexus. If you've been modding games like Fallout 3 or Skyrim, you may already be familiar with the Nexus Network. It allows for incredibly easy modding tools, removing a lot of the hassle that used to be associated with mods. Hell, there's already something on there! People, man. They're awesome.