I like the way Lua handles strings and numbers quite a bit. They're different types, but arithmetic will convert a string to a number when it can.

This is without footguns, because concatenation is a different operator entirely.

    2 + "3"  -- 5 
    2 .. "3" -- "23"

It's rather convenient, especially when you can combine it with LPeg to parse files with numbers in them, then do the maths directly.