s7 Scheme is as easy to embed as Lua, you might like it. I used it for Scheme for Max and Scheme for Pd and it's been wonderful - it was the easiest to embed of a bunch of lisps I tried. It's not well known because it came out of the computer music world, but it has also been used in games and other media tools.

Janet is surprisingly similar to s7 in many ways. I've been keeping my eyes on it as well, I sure hope it continues! Schemes are so flexible that moving from one to another is just not that hard.