I'm grateful for the author's "other options that were considered" section with eight alternatives to S7. But Embeddable Common Lisp (ECL) is the only one listed that he doesn't write a few sentences about, to contrast its pros and cons versus S7. I'd love to hear more.

clang and ECL both seem interesting, as long as LGPL license is ok. They both are complex to embed though - neither are well tuned to be embedded in other applications. (I've been exploring on MacOS). Julia could be interesting too under same questions (and a better license for commercial products) but similarly has a fair bit of glue code needed - especially if you want to restrict (say) filesystem access.