This is gonna be subjective, because it depends on what your priorities are.

The two alternatives at the top of my list are Gravity and Wren. They are both designed for the same general profile that Lua has—a scripting language, safe to use, embeddable, with a small VM (low code size).

- https://github.com/marcobambini/gravity

- https://wren.io/

The language design choices are nice and familiar to people who are used to other existing languages. Lua is a bit radical.

Two other options are AngelScript and Squirrel, which are both a bit older and more mature than Gravity and Wren.

- http://www.angelcode.com/angelscript/

- http://squirrel-lang.org/

Finally, it’s much more feasible these days to embed something like Mono, and Guile has gotten a lot better.