Mjolnir is an OS X app that lets you automate common tasks using the language Lua. At its core, it doesn't actually do anything besides load up a Lua environment; the real power lies in all the useful modules that you can install.
You write a "config", which just means ~/.mjolnir/init.lua. This file, along with whatever modules it requires, have full access to the built-in mjolnir module, and all Lua modules that you have installed (e.g. from LuaRocks or any way you want to install them).
Mac OS X 10.8,
Mac OS X 10.9,
Mac OS X 10.10