Yattattack is a project mainly written in Lua, it's free.
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To run yattattack.wlua, you'll need:
On Windows, you can get all this and more by installing Lua for Windows.
Outside of Windows, check your local package manager (which will most likely have packages for Lua) and/or Sourceforge (there are some good tips out there for setting up the files you can get from Sourceforge if you search for them).