I really like the sound of Wren, but you may also want to look into Squirrel, it's basically Lua re-imagined/reimplemented but without all the Lua quirks and with C-style syntax (but it still has optional lua-style prototypes, which means it ends up very similar to Javascript). Its embedding API is largely a copy of Lua's. There is also an active fork called Quirrel that makes the language more like Python.

There are loads of scripting languages but very few of them have an embedding API as powerful as Lua or Squirrel's. (My benchmarks: what's the overhead of a userdata pointer? Is there a proper debug API? Can you suspend a co-routine from inside a called C function? Very few languages even have coroutines.) Last I looked at it years ago, Wren was one of the best. Of course, the most featureful embedding API of all belongs to LuaJIT.

Yeah, Lua's implementation is fantastic - but the language is "quirky" at best.

Wren looks a bit more orthodox, although it's heavily built around class-based OOP - you can't even define and call a top-level function without extra syntax to (1) turn it into an object, and (2) call one of that object's methods:

  var sayHello = Fn.new { System.print("hello") }
  sayHello.call() //> hello