it's trivial to implement a REPL yourself, you "just" need to poll for stdin in your main loop and pass this to S7 for evaluation. I made a demo once upon a time live coding with DearImGui: https://www.youtube.com/watch?v=MgHsl0u26MY

For the emacs side I used cmuscheme which is basically comint. Of course you don't get the same experience as in common lisp, but I found S7 to be pleasant to work with also in regards to reporting errors etc