If I get it right, MoonScript aims at doing the same for Lua. The difference is that (1) Lua ecosystem isn't nearly as unavoidable as JS' and (2) Although some design decisions in Lua aren't consensual, the one thing you cannot call the language is "messy". IMO, Lua's main drawback is that by being so flexible and lacking an interventionist benevolent dictator, it doesn't grow standard coding practices, as Python does. Of course, creating alternative syntaxes isn't likely to improve the matter.
But in the end, it's fun to write compilers, and this is a perfectly legitimate reason to write one.
MoonScript also gets rid of a lot of the more verbose parts of lua, and replaces them with CoffeeScript-like versions. For example: shorter anonymous function syntax, syntactically significant whitespace, default local variables.