"Ferret is a free software lisp implementation designed to be used in real time embedded control systems. Ferret lisp compiles down to self contained C++11"
"Easy FFI (Inline C,C++. See Accessing C,C++ Libraries)"
"Easily Embeddable (i.e Ferret fns are just C++ functors.)"
"Clasp is a new Common Lisp implementation that seamlessly interoperates with C++ libraries and programs using LLVM for compilation to native code."
Embeddable Common Lisp is a conforming implementation. It's what it says in the title, pretty much any Common Lisp library and still embeddable in C/C++. Use it with SLIME and all that.
I do like exo-lisps like Fennel, Ferret and Hy. They just have very different goals from the project referenced in this article.
Embedding Fennel in Rust allows you to ship user-facing macros written in Fennel without users having to setup a Lua environment beforehand (e.g. ).
I'm one of ECL maintainers, if you have questions about the implementation itself then I'll be happy to answer.