Interesting multi-page post on "Too many programming languages", especially interesting discussions on the XMOS, and the reference to ulisp. It just so happens that I am writing a Lisp interpreter in modern C++ and it has now been uploaded to github with the MIT license. No garbage collection yet - I will be adding one probably using shared_ptr. It uses boost variant and some lambda functions. At around 800 lines with comments and empty lines, it's not the smallest lisp, but it does support full Lisp semantics, e.g. a few tiny Lisp use vectors to store the cells, which would preclude them from supporting garbage collection.
Check it out if you like!
https://github.com/richardman/cppLisp. Maybe you will find it interesting or even useful.