An "JIT interpreter" for Emacs Lisp [1] with Graal Truffle [2] in Java. And it is really amazing how the frameworks these days simplify building a JIT runtime for a language. Currently I'm working on a pdump[3]-like feature for it.
[1] https://codeberg.org/gudzpoz/Juicemacs/src/branch/main/elisp
[2] https://www.graalvm.org/latest/graalvm-as-a-platform/languag...
[3] https://www.gnu.org/software/emacs/manual/html_node/elisp/Bu...