I'm currently using a CPU-slow machine, and I've discovered everything is slow among the popular scripting languages, except Lua. I've thought JS has good startup time, but some of my Lua scripts that are doing file i/o finish faster than node.js does a ‘hello world.’ Lua is also very lightweight on memory, to my knowledge. I think it can even do true multithreading, via libraries.

So, there's a Lisp on top of Lua―compiled, not interpreted: https://fennel-lang.org

It's deliberately feature-poor, just like Lua: you use libraries for everything aside simple functions and loops. And it suffers somewhat from double unpopularity of Lua and Lisp. But it works fine.