Scheme's a very decent language too, but so far I haven't found any scheme implementations out there which are anywhere near as good as Lua—small, portable, hig

Scheme's a very decent language too, but so far I haven't found any scheme implementations out there which are anywhere near as good as Lua—small, portable, highly efficient, robust, easy to integrate [with the "underlying" program], well maintained, good and active community, etc—for this space. The most popular scheme implementations tend to be enormous, despite the language's historical reputation as a "small" language. Lua's a great language, but the amazingly good implementation is as much (or more) a factor than the language itself.