People who know me personally know how much I love Io's design and how its applied philosophy of minimalism inspired me. Io is (to some extent) inspired from Lua, which is also a very lightweight embedded language. Lua is well-known for being used as an embedded scripting language in C++ application, one of them notoriously being WoW. Lua also happens to be reasonably fast, to have a nice Pascal-inspired syntax and has some very interesting projects such as Meta-Lua.

So having all those advantages (including closures and corountines), how come Lua is not as widespread as say, Python ? I'd say the answer is this: there is no real standard library, and as opposed to Python, Lua doesn't come with batteries included.

Now, things can change: we all know that Java is one of the language with the most libraries, which has an OK VM. There is already Python, Ruby and a handful of other dynamic languages... but now Lua is also available in the form of Kahlua. True to the original Lua, Kahlua is very small (source is <50K) and fully compatible with the original Lua.

I see this as a great opportunity to use Lua a little bit more in practice, and take advantage of the richness of the JVM and the lightweightness of Lua. This also leads to another question: do you really use a language for its syntax, for its library or for its implementation ?