LuaJIT is great, and with the real fast and easy to use FFI it makes you design, prototype, test, and write real applications dealing with lots of "C" libraries

LuaJIT is great, and with the real fast and easy to use FFI it makes you design, prototype, test, and write real applications dealing with lots of "C" libraries much much easier. I think the only real drawback, and maybe its being worked on (haven't checked the project in several months) is the internal memory limit of the lua heap (has to be below the first addressable 4GB's).